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,
+    };
+  }
+}