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>

tests/unit/models/database/test_marketplace_import_job.py

@@ -3,7 +3,7 @@
 
 import pytest
 
-from models.database.marketplace_import_job import MarketplaceImportJob
+from app.modules.marketplace.models import MarketplaceImportJob
 
 
 @pytest.mark.unit

tests/unit/models/database/test_marketplace_product.py

@@ -4,8 +4,8 @@
 import pytest
 from sqlalchemy.exc import IntegrityError
 
-from models.database.marketplace_product import MarketplaceProduct
-from models.database.marketplace_product_translation import (
+from app.modules.marketplace.models import (
+    MarketplaceProduct,
     MarketplaceProductTranslation,
 )
 

tests/unit/models/database/test_product.py

@@ -4,7 +4,7 @@
 import pytest
 from sqlalchemy.exc import IntegrityError
 
-from models.database.product import Product
+from app.modules.catalog.models import Product
 
 
 @pytest.mark.unit