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/admin.py

@@ -189,6 +189,27 @@ def get_stats(db: Session = Depends(get_db)):
     }
 
 
+@router.post("/trigger-images", status_code=200)
+def trigger_images(
+    limit: int = 10,
+    missing_only: bool = True,
+    force: bool = False,
+    recipe_id: Optional[UUID] = None,
+    db: Session = Depends(get_db),
+):
+    from app.services.image_generation import generate_images_batch
+
+    recipe_ids = [str(recipe_id)] if recipe_id else None
+    result = generate_images_batch(
+        db,
+        recipe_ids=recipe_ids,
+        missing_only=missing_only,
+        force=force,
+        limit=limit,
+    )
+    return result
+
+
 @router.post("/trigger-discovery", status_code=200)
 def trigger_discovery(
     family_profile_id: UUID,