refactor: migrate models to canonical module locations

- Move Product/ProductTranslation to app/modules/catalog/models/
- Move VendorOnboarding to app/modules/marketplace/models/
- Delete legacy re-export files for marketplace models:
  - letzshop.py, marketplace.py, marketplace_product.py
  - marketplace_product_translation.py, marketplace_import_job.py
- Delete legacy product.py, product_translation.py, onboarding.py
- Update all imports across services, tasks, tests to use module locations

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/services/letzshop/order_service.py

@@ -16,15 +16,15 @@ from sqlalchemy.orm import Session
 
 from app.services.order_service import order_service as unified_order_service
 from app.services.subscription_service import subscription_service
-from models.database.letzshop import (
+from app.modules.marketplace.models import (
     LetzshopFulfillmentQueue,
     LetzshopHistoricalImportJob,
     LetzshopSyncLog,
+    MarketplaceImportJob,
     VendorLetzshopCredentials,
 )
-from models.database.marketplace_import_job import MarketplaceImportJob
 from app.modules.orders.models import Order, OrderItem
-from models.database.product import Product
+from app.modules.catalog.models import Product
 from models.database.vendor import Vendor
 
 logger = logging.getLogger(__name__)