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/integration/tasks/test_background_tasks.py

@@ -4,7 +4,7 @@ from unittest.mock import AsyncMock, MagicMock, patch
 import pytest
 
 from app.tasks.background_tasks import process_marketplace_import
-from models.database.marketplace_import_job import MarketplaceImportJob
+from app.modules.marketplace.models import MarketplaceImportJob
 
 
 @pytest.mark.integration

tests/integration/tasks/test_letzshop_tasks.py

@@ -8,7 +8,7 @@ import pytest
 
 from app.services.letzshop import LetzshopClientError
 from app.tasks.letzshop_tasks import process_historical_import
-from models.database.letzshop import LetzshopHistoricalImportJob
+from app.modules.marketplace.models import LetzshopHistoricalImportJob
 
 
 @pytest.fixture