feat(backend): wire exclude_recipe_ids, verify MealPlan votes schema, add image generation service

- api/meal_plans.py: /regenerate now passes exclude_recipe_ids into generate_meal_plan
- planner/generate.py: filter recipe_dicts by exclude_recipe_ids set
- image_generation.py: OpenAI gpt-image-1 client with prompt building, b64_json handling
- main.py: StaticFiles mount at /static for generated images
- admin.py: POST /api/admin/trigger-images endpoint for batch generation
- scripts/generate_images.py: CLI for batch image generation
- docker-compose.yml + nginx: volume mounts for static/images persistence
- Verify MealPlanItem.votes ↔ MealPlanVote relationship is correct; no model bug exists

backend/app/api/meal_plans.py

@@ -92,9 +92,6 @@ def regenerate(payload: RegenerateRequest, db: Session = Depends(get_db)) -> Gen
     if payload.relax_max_meal_cost is not None:
         config = replace(config, max_meal_cost=payload.relax_max_meal_cost)
 
-    # exclude_recipe_ids accepted for forward-compat but not yet honored.
-    # See plan §Open items.
-
     db.query(MealPlan).filter(
         MealPlan.family_profile_id == payload.family_profile_id,
         MealPlan.week_start_date == payload.week_start_date,
@@ -106,6 +103,7 @@ def regenerate(payload: RegenerateRequest, db: Session = Depends(get_db)) -> Gen
         family_id=payload.family_profile_id,
         week_start_date=payload.week_start_date,
         config=config,
+        exclude_recipe_ids=set(payload.exclude_recipe_ids) if payload.exclude_recipe_ids else None,
     )
     items = (
         db.query(MealPlanItem)