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/services/test_marketplace_service.py

@@ -12,7 +12,7 @@ from app.exceptions.marketplace_import_job import (
 )
 from app.exceptions.vendor import UnauthorizedVendorAccessException
 from app.services.marketplace_import_job_service import MarketplaceImportJobService
-from models.database.marketplace_import_job import MarketplaceImportJob
+from app.modules.marketplace.models import MarketplaceImportJob
 from models.schema.marketplace_import_job import MarketplaceImportJobRequest
 
 
@@ -283,7 +283,7 @@ class TestMarketplaceImportJobService:
         self, db, test_marketplace_import_job, test_vendor
     ):
         """Test converting database model to response model."""
-        from models.database.marketplace_import_job import MarketplaceImportJob as MIJ
+        from app.modules.marketplace.models import MarketplaceImportJob as MIJ
 
         # Re-query to get fresh instance with relationships
         job = db.query(MIJ).filter(MIJ.id == test_marketplace_import_job.id).first()