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>

models/database/__init__.py

@@ -57,13 +57,18 @@ from app.modules.orders.models import (
     VATRegime,
     VendorInvoiceSettings,
 )
-from .letzshop import (
+from app.modules.marketplace.models import (
     LetzshopFulfillmentQueue,
     LetzshopHistoricalImportJob,
     LetzshopSyncLog,
     VendorLetzshopCredentials,
+    MarketplaceImportError,
+    MarketplaceImportJob,
+    DigitalDeliveryMethod,
+    MarketplaceProduct,
+    ProductType,
+    MarketplaceProductTranslation,
 )
-from .marketplace_import_job import MarketplaceImportError, MarketplaceImportJob
 from app.modules.messaging.models import (
     Conversation,
     ConversationParticipant,
@@ -72,18 +77,11 @@ from app.modules.messaging.models import (
     MessageAttachment,
     ParticipantType,
 )
-from .marketplace_product import (
-    DigitalDeliveryMethod,
-    MarketplaceProduct,
-    ProductType,
-)
 from .media import MediaFile, ProductMedia
-from .marketplace_product_translation import MarketplaceProductTranslation
-from .onboarding import OnboardingStatus, OnboardingStep, VendorOnboarding
+from app.modules.marketplace.models import OnboardingStatus, OnboardingStep, VendorOnboarding
 from app.modules.orders.models import Order, OrderItem
 from app.modules.orders.models import OrderItemException
-from .product import Product
-from .product_translation import ProductTranslation
+from app.modules.catalog.models import Product, ProductTranslation
 from .subscription import (
     AddOnCategory,
     AddOnProduct,