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/modules/billing/models/__init__.py

@@ -11,6 +11,8 @@ Usage:
         SubscriptionTier,
         SubscriptionStatus,
         TierCode,
+        Feature,
+        FeatureCode,
     )
 """
 
@@ -31,14 +33,23 @@ from app.modules.billing.models.subscription import (
     # Legacy constants
     TIER_LIMITS,
 )
+from app.modules.billing.models.feature import (
+    # Enums
+    FeatureCategory,
+    FeatureUILocation,
+    # Model
+    Feature,
+    # Constants
+    FeatureCode,
+)
 
 __all__ = [
-    # Enums
+    # Subscription Enums
     "TierCode",
     "SubscriptionStatus",
     "AddOnCategory",
     "BillingPeriod",
-    # Models
+    # Subscription Models
     "SubscriptionTier",
     "AddOnProduct",
     "VendorAddOn",
@@ -48,4 +59,11 @@ __all__ = [
     "CapacitySnapshot",
     # Legacy constants
     "TIER_LIMITS",
+    # Feature Enums
+    "FeatureCategory",
+    "FeatureUILocation",
+    # Feature Model
+    "Feature",
+    # Feature Constants
+    "FeatureCode",
 ]