feat(backend): persist plan scores on MealPlanItem

- Migration 0012 adds score (float) and components (jsonb) to meal_plan_item
- generate.py: populates score and components at create time
- schemas/MealPlanItemResponse: include score + components fields
- GET /api/meal-plans/{id}: returns persisted values instead of zeros

backend/app/schemas/__init__.py

@@ -188,6 +188,8 @@ class MealPlanItemResponse(MealPlanItemBase):
     denial_reason: Optional[DenialReason] = None
     denial_details: Optional[str] = None
     used_pantry_items: Optional[List[UUID]] = []
+    score: Optional[float] = None
+    components: Optional[Dict[str, float]] = None
     created_at: Optional[datetime] = None
     updated_at: Optional[datetime] = None
     recipe: Optional[RecipeResponse] = None