feat: add rematch functionality for recipe ingredients and enhance inventory management

- Added a new API path for rematching recipe ingredients in `api_paths.dart`.
- Implemented a manual product creation dialog in `inventory_screen.dart` to allow users to create new products directly.
- Integrated the rematch functionality in `recipe_repository.dart` to handle rematching of recipe ingredients.
- Updated the recipe detail screen to include a button for triggering the rematch process.
- Introduced a new `RecipeMatchingService` in the backend to handle ingredient matching logic.
- Added database migration to include `aiEngineEnabled` column in the User table.

Co-authored-by: Copilot <copilot@github.com>

backend/src/receipt-import/receipt-import.service.ts

@@ -159,7 +159,7 @@ export class ReceiptImportService {
     const matched = await this.matchProducts(rawItems, userId);
 
     // Steg 3: Regel + AI-kategorisering för alla användare
-    return this.enrichWithAiCategories(matched);
+    return this.enrichWithAiCategories(matched, userId);
   }
 
   private async parseReceiptViaImporter(file: Express.Multer.File): Promise<ParsedReceiptItem[]> {
@@ -341,7 +341,7 @@ export class ReceiptImportService {
     return best?.product;
   }
 
-  private async enrichWithAiCategories(items: ParsedReceiptItem[]): Promise<ParsedReceiptItem[]> {
+  private async enrichWithAiCategories(items: ParsedReceiptItem[], userId?: number): Promise<ParsedReceiptItem[]> {
     let categories: Awaited<ReturnType<CategoriesService['findFlattened']>>;
     try {
       categories = await this.categoriesService.findFlattened();
@@ -349,6 +349,13 @@ export class ReceiptImportService {
       return items; // Om kategoritjänsten är otillgänglig, returnera utan AI-förslag
     }
 
+    const user = userId
+      ? await this.prisma.user.findUnique({
+          where: { id: userId },
+          select: { aiEngineEnabled: true },
+        })
+      : null;
+
     const enriched: ParsedReceiptItem[] = [];
     for (const item of items) {
       if (!item.rawName) {
@@ -424,9 +431,13 @@ export class ReceiptImportService {
 
         // AI används som fallback när varken matchning eller regler satte kategori
         if (!nextSuggestion) {
-          pushTrace('ai invoked');
-          nextSuggestion = await this.aiService.suggestCategory(item.rawName, categories);
-          pushTrace(`ai result -> "${nextSuggestion.path}" (${nextSuggestion.confidence})`);
+          if (user?.aiEngineEnabled) {
+            pushTrace('ai invoked');
+            nextSuggestion = await this.aiService.suggestCategory(item.rawName, categories);
+            pushTrace(`ai result -> "${nextSuggestion.path}" (${nextSuggestion.confidence})`);
+          } else {
+            pushTrace('ai skipped, feature disabled');
+          }
         } else {
           pushTrace(`ai skipped, current -> "${nextSuggestion.path}"`);
         }