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>

models/database/__init__.py

@@ -48,7 +48,7 @@ from app.modules.customers.models import PasswordResetToken
 from .email import EmailCategory, EmailLog, EmailStatus, EmailTemplate
 from .vendor_email_template import VendorEmailTemplate
 from .vendor_email_settings import EmailProvider, VendorEmailSettings, PREMIUM_EMAIL_PROVIDERS
-from .feature import Feature, FeatureCategory, FeatureCode, FeatureUILocation
+from app.modules.billing.models import Feature, FeatureCategory, FeatureCode, FeatureUILocation
 from app.modules.inventory.models import Inventory
 from app.modules.inventory.models import InventoryTransaction, TransactionType
 from app.modules.orders.models import (
@@ -77,7 +77,8 @@ from app.modules.messaging.models import (
     MessageAttachment,
     ParticipantType,
 )
-from .media import MediaFile, ProductMedia
+from .media import MediaFile
+from app.modules.catalog.models import ProductMedia
 from app.modules.marketplace.models import OnboardingStatus, OnboardingStep, VendorOnboarding
 from app.modules.orders.models import Order, OrderItem
 from app.modules.orders.models import OrderItemException