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/catalog/models/__init__.py

@@ -5,13 +5,15 @@ Catalog module models.
 This is the canonical location for product models.
 
 Usage:
-    from app.modules.catalog.models import Product, ProductTranslation
+    from app.modules.catalog.models import Product, ProductTranslation, ProductMedia
 """
 
 from app.modules.catalog.models.product import Product
 from app.modules.catalog.models.product_translation import ProductTranslation
+from app.modules.catalog.models.product_media import ProductMedia
 
 __all__ = [
     "Product",
     "ProductTranslation",
+    "ProductMedia",
 ]

app/modules/catalog/models/product_media.py

@@ -0,0 +1,71 @@
+# app/modules/catalog/models/product_media.py
+"""
+Product-Media association model.
+
+Links media files to products with usage type tracking
+(main image, gallery, variant images, etc.)
+"""
+
+from sqlalchemy import (
+    Column,
+    ForeignKey,
+    Index,
+    Integer,
+    String,
+    UniqueConstraint,
+)
+from sqlalchemy.orm import relationship
+
+from app.core.database import Base
+from models.database.base import TimestampMixin
+
+
+class ProductMedia(Base, TimestampMixin):
+    """Association between products and media files.
+
+    Tracks which media files are used by which products,
+    including the usage type (main image, gallery, variant, etc.)
+    """
+
+    __tablename__ = "product_media"
+
+    id = Column(Integer, primary_key=True, index=True)
+    product_id = Column(
+        Integer,
+        ForeignKey("products.id", ondelete="CASCADE"),
+        nullable=False,
+    )
+    media_id = Column(
+        Integer,
+        ForeignKey("media_files.id", ondelete="CASCADE"),
+        nullable=False,
+    )
+
+    # Usage type
+    usage_type = Column(String(50), nullable=False, default="gallery")
+    # Types: main_image, gallery, variant, thumbnail, swatch
+
+    # Display order for galleries
+    display_order = Column(Integer, default=0)
+
+    # Variant-specific (if usage_type is variant)
+    variant_id = Column(Integer)  # Reference to variant if applicable
+
+    # Relationships
+    product = relationship("Product")
+    media = relationship("MediaFile", back_populates="product_associations")
+
+    __table_args__ = (
+        UniqueConstraint(
+            "product_id", "media_id", "usage_type",
+            name="uq_product_media_usage"
+        ),
+        Index("idx_product_media_product", "product_id"),
+        Index("idx_product_media_media", "media_id"),
+    )
+
+    def __repr__(self):
+        return (
+            f"<ProductMedia(product_id={self.product_id}, "
+            f"media_id={self.media_id}, usage='{self.usage_type}')>"
+        )