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/fixtures/marketplace_import_job_fixtures.py

@@ -8,7 +8,7 @@ See tests/conftest.py for details on fixture best practices.
 
 import pytest
 
-from models.database.marketplace_import_job import MarketplaceImportJob
+from app.modules.marketplace.models import MarketplaceImportJob
 
 
 @pytest.fixture

tests/fixtures/marketplace_product_fixtures.py

@@ -13,8 +13,8 @@ import uuid
 
 import pytest
 
-from models.database.marketplace_product import MarketplaceProduct
-from models.database.marketplace_product_translation import (
+from app.modules.marketplace.models import (
+    MarketplaceProduct,
     MarketplaceProductTranslation,
 )
 

tests/fixtures/vendor_fixtures.py

@@ -12,7 +12,7 @@ import pytest
 
 from models.database.company import Company
 from app.modules.inventory.models import Inventory
-from models.database.product import Product
+from app.modules.catalog.models import Product
 from models.database.vendor import Vendor