refactor: migrate Feature to billing module and split ProductMedia to catalog

- Move Feature model from models/database/ to app/modules/billing/models/
  (tightly coupled to SubscriptionTier for tier-based access control)
- Move ProductMedia from models/database/media.py to app/modules/catalog/models/
  (product-specific media associations belong with catalog)
- Keep MediaFile as CORE in models/database/media.py (cross-cutting file storage)
- Convert legacy feature.py to re-export for backwards compatibility
- Update all imports to use canonical module locations

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/services/feature_service.py

@@ -34,7 +34,7 @@ from app.exceptions.feature import (
     InvalidFeatureCodesError,
     TierNotFoundError,
 )
-from models.database.feature import Feature, FeatureCode
+from app.modules.billing.models import Feature, FeatureCode
 from app.modules.billing.models import SubscriptionTier, VendorSubscription
 
 logger = logging.getLogger(__name__)

app/services/media_service.py

@@ -27,7 +27,8 @@ from app.exceptions.media import (
     UnsupportedMediaTypeException,
     MediaFileTooLargeException,
 )
-from models.database.media import MediaFile, ProductMedia
+from models.database.media import MediaFile
+from app.modules.catalog.models import ProductMedia
 
 logger = logging.getLogger(__name__)