feat(ai): enhance AI trace warnings and reason codes system

- Added structured warning system with `AdminAiWarning` type in backend and Flutter
- Implemented detailed reason descriptors with `FlyerReasonDescriptor` for parse and match operations
- Added `legacyWarnings` field to maintain backward compatibility
- Enhanced AI trace service to collect and format warnings with item-level context
- Updated flyer import services to include detailed reason descriptions in responses
- Added Swedish diacritic preservation for cheese variants (Prästost, Herrgårdsost, Grevéost)
- Implemented UTF-8 content validation for AI responses
- Added new reason code definitions in `reason-codes.ts`
- Updated Flutter UI to display structured warnings with severity indicators
- Added error report generation and copy functionality in admin panel
- Added comprehensive test coverage for new warning system and cheese normalization

BREAKING CHANGE: AI trace warnings are now structured objects instead of simple strings

flutter/lib/features/import/domain/flyer_import_item.dart

@@ -1,4 +1,6 @@
-class FlyerImportItem {
+import 'flyer_reason_descriptor.dart';
+
+class FlyerImportItem {
   final int? flyerItemId;
   final String rawName;
   final String normalizedName;
@@ -12,11 +14,14 @@ class FlyerImportItem {
   final double? comparisonPrice;
   final String? comparisonUnit;
   final double? parseConfidence;
-  final List<String> parseReasons;
-  final int? matchedProductId;
-  final String? matchedProductName;
-  final String? matchedVia;
-  final double? matchConfidence;
+  final List<String> parseReasons;
+  final List<FlyerReasonDescriptor> parseReasonsDetailed;
+  final int? matchedProductId;
+  final String? matchedProductName;
+  final String? matchedVia;
+  final double? matchConfidence;
+  final List<String> matchReasons;
+  final List<FlyerReasonDescriptor> matchReasonsDetailed;
 
   FlyerImportItem({
     required this.flyerItemId,
@@ -31,13 +36,16 @@ class FlyerImportItem {
     this.offerLimitText,
     this.comparisonPrice,
     this.comparisonUnit,
-    this.parseConfidence,
-    this.parseReasons = const [],
-    this.matchedProductId,
-    this.matchedProductName,
-    this.matchedVia,
-    this.matchConfidence,
-  });
+    this.parseConfidence,
+    this.parseReasons = const [],
+    this.parseReasonsDetailed = const [],
+    this.matchedProductId,
+    this.matchedProductName,
+    this.matchedVia,
+    this.matchConfidence,
+    this.matchReasons = const [],
+    this.matchReasonsDetailed = const [],
+  });
 
   factory FlyerImportItem.fromJson(Map<String, dynamic> json) {
     return FlyerImportItem(
@@ -53,12 +61,25 @@ class FlyerImportItem {
       offerLimitText: json['offerLimitText'] as String?,
       comparisonPrice: (json['comparisonPrice'] as num?)?.toDouble(),
       comparisonUnit: json['comparisonUnit'] as String?,
-      parseConfidence: (json['parseConfidence'] as num?)?.toDouble(),
-      parseReasons: (json['parseReasons'] as List?)?.map((e) => e.toString()).toList() ?? const [],
-      matchedProductId: (json['matchedProductId'] as num?)?.toInt(),
-      matchedProductName: json['matchedProductName'] as String?,
-      matchedVia: json['matchedVia'] as String?,
-      matchConfidence: (json['matchConfidence'] as num?)?.toDouble(),
+      parseConfidence: (json['parseConfidence'] as num?)?.toDouble(),
+      parseReasons: (json['parseReasons'] as List?)?.map((e) => e.toString()).toList() ?? const [],
+      parseReasonsDetailed:
+          (json['parseReasonsDetailed'] as List?)
+                  ?.whereType<Map>()
+                  .map((e) => FlyerReasonDescriptor.fromJson(Map<String, dynamic>.from(e)))
+                  .toList() ??
+              const [],
+      matchedProductId: (json['matchedProductId'] as num?)?.toInt(),
+      matchedProductName: json['matchedProductName'] as String?,
+      matchedVia: json['matchedVia'] as String?,
+      matchConfidence: (json['matchConfidence'] as num?)?.toDouble(),
+      matchReasons: (json['matchReasons'] as List?)?.map((e) => e.toString()).toList() ?? const [],
+      matchReasonsDetailed:
+          (json['matchReasonsDetailed'] as List?)
+                  ?.whereType<Map>()
+                  .map((e) => FlyerReasonDescriptor.fromJson(Map<String, dynamic>.from(e)))
+                  .toList() ??
+              const [],
     );
   }
 
@@ -78,10 +99,15 @@ class FlyerImportItem {
       'comparisonUnit': comparisonUnit,
       'parseConfidence': parseConfidence,
       'parseReasons': parseReasons,
+      'parseReasonsDetailed':
+          parseReasonsDetailed.map((reason) => reason.toJson()).toList(),
       'matchedProductId': matchedProductId,
       'matchedProductName': matchedProductName,
       'matchedVia': matchedVia,
       'matchConfidence': matchConfidence,
+      'matchReasons': matchReasons,
+      'matchReasonsDetailed':
+          matchReasonsDetailed.map((reason) => reason.toJson()).toList(),
     };
   }
 
@@ -105,10 +131,13 @@ class FlyerImportItem {
       comparisonUnit: comparisonUnit,
       parseConfidence: parseConfidence,
       parseReasons: parseReasons,
+      parseReasonsDetailed: parseReasonsDetailed,
       matchedProductId: matchedProductId,
       matchedProductName: matchedProductName,
       matchedVia: matchedVia,
       matchConfidence: matchConfidence,
+      matchReasons: matchReasons,
+      matchReasonsDetailed: matchReasonsDetailed,
     );
   }
 }

flutter/lib/features/import/domain/flyer_reason_descriptor.dart

@@ -0,0 +1,39 @@
+class FlyerReasonDescriptor {
+  final String code;
+  final String kind;
+  final String title;
+  final String message;
+  final String severity;
+  final String? location;
+
+  const FlyerReasonDescriptor({
+    required this.code,
+    required this.kind,
+    required this.title,
+    required this.message,
+    required this.severity,
+    required this.location,
+  });
+
+  factory FlyerReasonDescriptor.fromJson(Map<String, dynamic> json) {
+    return FlyerReasonDescriptor(
+      code: (json['code'] ?? '').toString(),
+      kind: (json['kind'] ?? '').toString(),
+      title: (json['title'] ?? '').toString(),
+      message: (json['message'] ?? '').toString(),
+      severity: (json['severity'] ?? '').toString(),
+      location: json['location']?.toString(),
+    );
+  }
+
+  Map<String, dynamic> toJson() {
+    return {
+      'code': code,
+      'kind': kind,
+      'title': title,
+      'message': message,
+      'severity': severity,
+      'location': location,
+    };
+  }
+}

flutter/lib/features/import/presentation/flyer_import_tab.dart

@@ -1,6 +1,6 @@
 import 'package:file_picker/file_picker.dart';
-import 'dart:typed_data';
 import 'package:flutter/material.dart';
+import 'package:flutter/services.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:go_router/go_router.dart';
 
@@ -14,6 +14,7 @@ import '../../shopping_list/data/shopping_list_providers.dart';
 import '../data/flyer_import_session.dart';
 import '../data/import_providers.dart';
 import '../domain/flyer_import_item.dart';
+import '../domain/flyer_reason_descriptor.dart';
 import '../domain/flyer_import_result.dart';
 import 'error_dialog.dart';
 
@@ -32,6 +33,7 @@ class _FlyerImportTabState extends ConsumerState<FlyerImportTab> {
   List<AdminCategoryNode> _categoryTree = const [];
   FlyerImportResult? _result;
   final Map<int, bool> _selected = {};
+  final Map<int, bool> _expandedReasonRows = {};
 
   @override
   void initState() {
@@ -90,6 +92,7 @@ class _FlyerImportTabState extends ConsumerState<FlyerImportTab> {
           _selected
             ..clear()
             ..addAll(selected);
+          _expandedReasonRows.clear();
         });
         await _loadRestoredSourceIfNeeded(serverResult, token);
         notifier.setImportedResult(
@@ -117,6 +120,7 @@ class _FlyerImportTabState extends ConsumerState<FlyerImportTab> {
           _selected
             ..clear()
             ..addAll(selected);
+          _expandedReasonRows.clear();
         });
         await _loadRestoredSourceIfNeeded(latest, token);
         notifier.setImportedResult(
@@ -130,6 +134,7 @@ class _FlyerImportTabState extends ConsumerState<FlyerImportTab> {
           _selected
             ..clear()
             ..addAll(session.selected);
+          _expandedReasonRows.clear();
         });
       }
     } catch (_) {
@@ -141,6 +146,7 @@ class _FlyerImportTabState extends ConsumerState<FlyerImportTab> {
         _selected
           ..clear()
           ..addAll(session.selected);
+        _expandedReasonRows.clear();
       });
     }
   }
@@ -196,6 +202,7 @@ class _FlyerImportTabState extends ConsumerState<FlyerImportTab> {
         _selected
           ..clear()
           ..addAll(selected);
+        _expandedReasonRows.clear();
       });
       ref.read(flyerImportSessionProvider.notifier).setImportedResult(
             result: parsed,
@@ -494,6 +501,39 @@ class _FlyerImportTabState extends ConsumerState<FlyerImportTab> {
     );
   }
 
+  Future<void> _copyText(String value, String label) async {
+    await Clipboard.setData(ClipboardData(text: value));
+    if (!mounted) return;
+    ScaffoldMessenger.of(context)
+        .showSnackBar(SnackBar(content: Text('$label kopierad')));
+  }
+
+  IconData _reasonSeverityIcon(String severity) {
+    switch (severity) {
+      case 'error':
+        return Icons.error_outline;
+      case 'warning':
+        return Icons.warning_amber_rounded;
+      default:
+        return Icons.info_outline;
+    }
+  }
+
+  Color _reasonSeverityColor(String severity) {
+    switch (severity) {
+      case 'error':
+        return Colors.red.shade700;
+      case 'warning':
+        return Colors.orange.shade700;
+      default:
+        return Colors.blue.shade700;
+    }
+  }
+
+  int _countWarningReasons(List<FlyerReasonDescriptor> reasons) {
+    return reasons.where((reason) => reason.severity == 'warning' || reason.severity == 'error').length;
+  }
+
   Widget _buildWarningsPanel(ThemeData theme) {
     final warnings = _result?.warnings ?? const <String>[];
     if (warnings.isEmpty) return const SizedBox.shrink();
@@ -526,10 +566,24 @@ class _FlyerImportTabState extends ConsumerState<FlyerImportTab> {
           const SizedBox(height: 8),
           ...warnings.map((warning) => Padding(
                 padding: const EdgeInsets.only(bottom: 4),
-                child: Text(
-                  '• $warning',
-                  style: theme.textTheme.bodySmall?.copyWith(
-                    color: Colors.amber.shade900,
+                child: InkWell(
+                  onTap: () => _copyText(warning, 'Varning'),
+                  borderRadius: BorderRadius.circular(4),
+                  child: Padding(
+                    padding: const EdgeInsets.symmetric(vertical: 2),
+                    child: Row(
+                      children: [
+                        Expanded(
+                          child: Text(
+                            '• $warning',
+                            style: theme.textTheme.bodySmall?.copyWith(
+                              color: Colors.amber.shade900,
+                            ),
+                          ),
+                        ),
+                        Icon(Icons.copy, size: 14, color: Colors.amber.shade800),
+                      ],
+                    ),
                   ),
                 ),
               )),
@@ -672,6 +726,12 @@ class _FlyerImportTabState extends ConsumerState<FlyerImportTab> {
               final sanitizedOfferText = item.offerText == null
                   ? ''
                   : _removeLimitTextFromOfferText(item.offerText!, limitText);
+              final detailedReasons = [
+                ...item.parseReasonsDetailed,
+                ...item.matchReasonsDetailed,
+              ];
+              final warningCount = _countWarningReasons(detailedReasons);
+              final reasonExpanded = _expandedReasonRows[index] == true;
 
               return CheckboxListTile(
                 value: _selected[index] ?? false,
@@ -720,6 +780,100 @@ class _FlyerImportTabState extends ConsumerState<FlyerImportTab> {
                     if (sanitizedOfferText.isNotEmpty) Text(sanitizedOfferText),
                     if (item.matchedProductName != null)
                       Text('Match: ${item.matchedProductName}'),
+                    if (detailedReasons.isNotEmpty) ...[
+                      const SizedBox(height: 6),
+                      InkWell(
+                        onTap: () => setState(
+                          () => _expandedReasonRows[index] = !reasonExpanded,
+                        ),
+                        child: Row(
+                          children: [
+                            Container(
+                              padding: const EdgeInsets.symmetric(
+                                  horizontal: 8, vertical: 3),
+                              decoration: BoxDecoration(
+                                color: warningCount > 0
+                                    ? Colors.orange.shade50
+                                    : Colors.blue.shade50,
+                                borderRadius: BorderRadius.circular(999),
+                                border: Border.all(
+                                  color: warningCount > 0
+                                      ? Colors.orange.shade200
+                                      : Colors.blue.shade200,
+                                ),
+                              ),
+                              child: Text(
+                                warningCount > 0
+                                    ? '$warningCount varningar'
+                                    : '${detailedReasons.length} info',
+                                style: theme.textTheme.labelSmall?.copyWith(
+                                  color: warningCount > 0
+                                      ? Colors.orange.shade900
+                                      : Colors.blue.shade900,
+                                  fontWeight: FontWeight.w700,
+                                ),
+                              ),
+                            ),
+                            const SizedBox(width: 8),
+                            Icon(
+                              reasonExpanded
+                                  ? Icons.expand_less
+                                  : Icons.expand_more,
+                              size: 18,
+                            ),
+                          ],
+                        ),
+                      ),
+                      if (reasonExpanded)
+                        ...detailedReasons.map(
+                          (reason) => Padding(
+                            padding: const EdgeInsets.only(top: 6),
+                            child: Row(
+                              crossAxisAlignment: CrossAxisAlignment.start,
+                              children: [
+                                Padding(
+                                  padding:
+                                      const EdgeInsets.only(top: 2, right: 6),
+                                  child: Icon(
+                                    _reasonSeverityIcon(reason.severity),
+                                    size: 16,
+                                    color: _reasonSeverityColor(
+                                      reason.severity,
+                                    ),
+                                  ),
+                                ),
+                                Expanded(
+                                  child: Column(
+                                    crossAxisAlignment:
+                                        CrossAxisAlignment.start,
+                                    children: [
+                                      Text(
+                                        reason.title,
+                                        style: theme.textTheme.bodySmall
+                                            ?.copyWith(
+                                          fontWeight: FontWeight.w700,
+                                        ),
+                                      ),
+                                      Text(
+                                        reason.message,
+                                        style: theme.textTheme.bodySmall,
+                                      ),
+                                      if ((reason.location ?? '').isNotEmpty)
+                                        Text(
+                                          reason.location!,
+                                          style: theme.textTheme.bodySmall
+                                              ?.copyWith(
+                                            color: theme.colorScheme.primary,
+                                          ),
+                                        ),
+                                    ],
+                                  ),
+                                ),
+                              ],
+                            ),
+                          ),
+                        ),
+                    ],
                   ],
                 ),
                 controlAffinity: ListTileControlAffinity.leading,