fix(receipt-import): surface create-product errors and harden response parsing

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

@@ -1,6 +1,7 @@
 import 'package:file_picker/file_picker.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
+import '../../../core/api/api_exception.dart';
 import '../../../core/api/api_paths.dart';
 import '../../../core/api/api_providers.dart';
 import '../../../core/ui/category_then_product_picker.dart';
@@ -370,7 +371,16 @@ class _EditDialogState extends State<_EditDialog> {
           _newProductNameCtrl.text.trim(),
           _newCategoryId!,
         );
-        if (newProduct == null || !mounted) return;
+        if (newProduct == null || !mounted) {
+          if (mounted) {
+            ScaffoldMessenger.of(context).showSnackBar(
+              const SnackBar(
+                content: Text('Kunde inte skapa produkten. Försök igen.'),
+              ),
+            );
+          }
+          return;
+        }
         if (!_localProducts.any((p) => p.id == newProduct.id)) {
           _localProducts = [..._localProducts, newProduct];
         }
@@ -379,6 +389,28 @@ class _EditDialogState extends State<_EditDialog> {
         _productCategoryId = _newCategoryId;
         _productCategoryPath = _newCategoryPath;
         _productCategorySource = _newCategorySource ?? CategorySelectionSource.manual;
+      } on ApiException catch (e) {
+        if (mounted) {
+          ScaffoldMessenger.of(context).showSnackBar(
+            SnackBar(
+              content: Text(
+                e.message.trim().isEmpty
+                    ? 'Kunde inte skapa produkten. Försök igen.'
+                    : e.message,
+              ),
+            ),
+          );
+        }
+        return;
+      } catch (_) {
+        if (mounted) {
+          ScaffoldMessenger.of(context).showSnackBar(
+            const SnackBar(
+              content: Text('Kunde inte skapa produkten. Försök igen.'),
+            ),
+          );
+        }
+        return;
       } finally {
         if (mounted) setState(() => _isCreatingProduct = false);
       }
@@ -997,27 +1029,44 @@ class _ReceiptImportTabState extends ConsumerState<ReceiptImportTab> {
         categoryTree: _categoryTree,
         initialEntryMode: initialEntryMode,
         onCreate: (name, categoryId) async {
-          try {
           final token = await ref.read(authStateProvider.future);
           final api = ref.read(apiClientProvider);
-            final data = await api.postJson(
+          final raw = await api.postJson(
             ProductApiPaths.createPrivate,
             body: {
               'name': name.trim(),
               'categoryId': categoryId,
             },
             token: token,
-            ) as Map<String, dynamic>;
-            final newProduct = (
-              id: data['id'] as int,
-              name: (data['canonicalName'] ?? data['name']) as String,
-              categoryId: categoryId,
           );
+
+          if (raw is! Map<String, dynamic>) {
+            throw Exception('Ogiltigt API-svar vid produktskapande.');
+          }
+
+          final idRaw = raw['id'];
+          if (idRaw is! num) {
+            throw Exception('API-svar saknar giltigt produkt-id.');
+          }
+
+          final displayNameRaw = raw['canonicalName'] ?? raw['name'];
+          final displayName = displayNameRaw?.toString().trim();
+          if (displayName == null || displayName.isEmpty) {
+            throw Exception('API-svar saknar produktnamn.');
+          }
+
+          final returnedCategoryId = raw['categoryId'] is num
+              ? (raw['categoryId'] as num).toInt()
+              : categoryId;
+
+          final newProduct = (
+            id: idRaw.toInt(),
+            name: displayName,
+            categoryId: returnedCategoryId,
+          );
+
           if (mounted) setState(() => _products = [..._products, newProduct]);
           return newProduct;
-          } catch (_) {
-            return null;
-          }
         },
       ),
     );