feat: add updateCategoryMine endpoint to manage product category updates

- Implemented a new PATCH endpoint in ProductsController to update the category of a user's product.
- Added corresponding service method in ProductsService to handle business logic and validation.
- Created UpdateCategoryMineDto for request validation.
- Enhanced error handling for forbidden actions and not found resources.
- Updated API error mapping in Flutter to handle specific forbidden messages.
- Modified ProductPickerField to allow product creation directly from the picker.
- Added tests for the new endpoint and service method to ensure proper functionality and error handling.

flutter/lib/core/api/api_error_mapper.dart

@@ -4,6 +4,11 @@ import 'package:flutter/services.dart';
 import '../l10n/l10n.dart';
 import 'api_exception.dart';
 
+const _safeForbiddenMessages = {
+  'Du kan inte omkategorisera, ta bort eller ändra produkter som är globala.',
+  'Du kan bara omkategorisera dina egna produkter',
+};
+
 String mapErrorToUserMessage(Object error, BuildContext context) {
   final l10n = context.l10n;
   if (error is ApiException) {
@@ -11,7 +16,9 @@ String mapErrorToUserMessage(Object error, BuildContext context) {
       case ApiErrorType.unauthorized:
         return l10n.sessionExpiredError;
       case ApiErrorType.forbidden:
-        return l10n.forbiddenError;
+        return _safeForbiddenMessages.contains(error.message)
+            ? error.message
+            : l10n.forbiddenError;
       case ApiErrorType.server:
         return l10n.serverError;
       case ApiErrorType.network:

flutter/lib/core/api/api_paths.dart

@@ -13,6 +13,7 @@ class ProductApiPaths {
   static const deleted = '/products/deleted';
   static const merge = '/products/merge';
   static const mergePrivate = '/products/private/merge';
+  static String updateMineCategory(int id) => '/products/mine/$id/category';
   static String mergePreview(int sourceProductId, int targetProductId) =>
       '/products/merge-preview?sourceProductId=$sourceProductId&targetProductId=$targetProductId';
   static String setStatus(int id) => '/products/$id/status';

flutter/lib/core/ui/product_picker_field.dart

@@ -36,6 +36,9 @@ class ProductPickerField extends StatelessWidget {
   /// If set, the picker bottom sheet opens with this text pre-filled in the search field.
   final String? initialQuery;
 
+  /// Optional callback to create a new product directly from the picker.
+  final Future<ProductOption?> Function(String name)? onCreate;
+
   const ProductPickerField({
     super.key,
     required this.products,
@@ -46,6 +49,7 @@ class ProductPickerField extends StatelessWidget {
     this.label = 'Produkt',
     this.errorText,
     this.initialQuery,
+    this.onCreate,
   });
 
   @override
@@ -57,7 +61,7 @@ class ProductPickerField extends StatelessWidget {
               orElse: () => null,
             );
 
-    final interactive = enabled && !isLoading && products.isNotEmpty;
+    final interactive = enabled && !isLoading && (products.isNotEmpty || onCreate != null);
 
     return MouseRegion(
       cursor: interactive ? SystemMouseCursors.click : MouseCursor.defer,
@@ -81,7 +85,9 @@ class ProductPickerField extends StatelessWidget {
               : selected == null
                   ? Text(
                       products.isEmpty
-                          ? 'Inga produkter tillgängliga'
+                          ? (onCreate != null
+                              ? 'Inga produkter tillgängliga. Tryck för att välja eller skapa.'
+                              : 'Inga produkter tillgängliga')
                           : 'Tryck för att välja produkt',
                     )
                   : Text(selected.name),
@@ -98,6 +104,7 @@ class ProductPickerField extends StatelessWidget {
       value: value,
       label: label,
       initialQuery: initialQuery,
+      onCreate: onCreate,
     );
     if (!context.mounted) return;
     if (result == null) return;