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/ai/ai.service.ts

@@ -13,10 +13,128 @@ export type CategorySuggestion = {
   usedFallback: boolean;
 };
 
+export type AiIngredientMatchSuggestion = {
+  productId: number;
+  reason?: string;
+  confidence: 'high' | 'medium' | 'low';
+};
+
+export type AiSubstitutionSuggestion = {
+  productId: number;
+  reason?: string;
+  confidence: 'high' | 'medium' | 'low';
+};
+
 @Injectable()
 export class AiService {
   private readonly logger = new Logger(AiService.name);
 
+  async suggestIngredientMatches(
+    rawIngredient: string,
+    candidates: Array<{ id: number; name: string; canonicalName?: string | null }>,
+  ): Promise<AiIngredientMatchSuggestion[]> {
+    const apiKey = process.env.MISTRAL_API_KEY;
+    if (!apiKey || candidates.length === 0) return [];
+
+    const candidateList = candidates
+      .map((c) => `[${c.id}] ${c.canonicalName || c.name}`)
+      .join('\n');
+
+    const systemPrompt = `Du matchar en ingrediensrad mot produktkandidater.
+Svara ENDAST med JSON: {"matches":[{"productId":123,"reason":"...","confidence":"high|medium|low"}]}
+Regler:
+1. Välj max 3 kandidater.
+2. Om inget passar, returnera tom lista.`;
+
+    const userPrompt = `Ingrediens: "${rawIngredient}"\nKandidater:\n${candidateList}`;
+
+    try {
+      const response = await fetch(MISTRAL_API_URL, {
+        method: 'POST',
+        headers: {
+          'Content-Type': 'application/json',
+          Authorization: `Bearer ${apiKey}`,
+        },
+        body: JSON.stringify({
+          model: MODEL,
+          messages: [
+            { role: 'system', content: systemPrompt },
+            { role: 'user', content: userPrompt },
+          ],
+          max_tokens: 300,
+          temperature: 0.1,
+          response_format: { type: 'json_object' },
+        }),
+      });
+
+      if (!response.ok) {
+        this.logger.warn(`suggestIngredientMatches API-fel: ${response.status}`);
+        return [];
+      }
+
+      const data = (await response.json()) as { choices: { message: { content: string } }[] };
+      const raw = data.choices?.[0]?.message?.content ?? '{}';
+      const parsed = JSON.parse(raw) as { matches?: AiIngredientMatchSuggestion[] };
+      return Array.isArray(parsed.matches) ? parsed.matches.slice(0, 3) : [];
+    } catch (err) {
+      this.logger.warn(`suggestIngredientMatches misslyckades: ${String(err)}`);
+      return [];
+    }
+  }
+
+  async suggestSubstitutions(
+    rawIngredient: string,
+    availableProducts: Array<{ id: number; name: string; canonicalName?: string | null }>,
+  ): Promise<AiSubstitutionSuggestion[]> {
+    const apiKey = process.env.MISTRAL_API_KEY;
+    if (!apiKey || availableProducts.length === 0) return [];
+
+    const productList = availableProducts
+      .map((p) => `[${p.id}] ${p.canonicalName || p.name}`)
+      .join('\n');
+
+    const systemPrompt = `Du föreslår ersättningsvaror för en ingrediens.
+Svara ENDAST med JSON: {"substitutions":[{"productId":123,"reason":"...","confidence":"high|medium|low"}]}
+Regler:
+1. Välj max 3 ersättningar.
+2. Om inget passar, returnera tom lista.`;
+
+    const userPrompt = `Ingrediens: "${rawIngredient}"\nTillgängliga produkter:\n${productList}`;
+
+    try {
+      const response = await fetch(MISTRAL_API_URL, {
+        method: 'POST',
+        headers: {
+          'Content-Type': 'application/json',
+          Authorization: `Bearer ${apiKey}`,
+        },
+        body: JSON.stringify({
+          model: MODEL,
+          messages: [
+            { role: 'system', content: systemPrompt },
+            { role: 'user', content: userPrompt },
+          ],
+          max_tokens: 300,
+          temperature: 0.2,
+          response_format: { type: 'json_object' },
+        }),
+      });
+
+      if (!response.ok) {
+        this.logger.warn(`suggestSubstitutions API-fel: ${response.status}`);
+        return [];
+      }
+
+      const data = (await response.json()) as { choices: { message: { content: string } }[] };
+      const raw = data.choices?.[0]?.message?.content ?? '{}';
+      const parsed = JSON.parse(raw) as { substitutions?: AiSubstitutionSuggestion[] };
+      return Array.isArray(parsed.substitutions) ? parsed.substitutions.slice(0, 3) : [];
+    } catch (err) {
+      this.logger.warn(`suggestSubstitutions misslyckades: ${String(err)}`);
+      return [];
+    }
+  }
+
   async suggestCategory(
     productName: string,
     categories: FlatCategory[],