refactor: product independence - remove inheritance pattern

Change Product/ProductTranslation from "override/inheritance" pattern
(NULL = inherit from marketplace) to "independent copy" pattern
(all fields populated at creation).

Key changes:
- Remove OVERRIDABLE_FIELDS, effective_* properties, reset_* methods
- Rename get_override_info() → get_source_comparison_info()
- Update copy_to_vendor_catalog() to copy ALL fields + translations
- Replace effective_* with direct field access in services
- Remove *_overridden fields from schema, keep *_source for comparison
- Add migration to populate NULL fields from marketplace products

The marketplace_product_id FK is kept for "view original source" feature.
Rollback tag: v1.0.0-pre-product-independence

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

tests/unit/models/database/test_product.py

@@ -130,103 +130,76 @@ class TestProductModel:
         assert product.marketplace_product is not None
         assert product.inventory_entries == []  # No inventory yet
 
-    def test_product_effective_properties(
+    def test_product_get_source_comparison_info(
         self, db, test_vendor, test_marketplace_product
     ):
-        """Test Product effective properties with override pattern."""
-        # First, set some values on the marketplace product
-        test_marketplace_product.price_numeric = 100.00
-        test_marketplace_product.brand = "SourceBrand"
-        db.commit()
-        db.refresh(test_marketplace_product)
+        """Test get_source_comparison_info method for 'view original source' feature.
 
-        # Create product without overrides
-        product = Product(
-            vendor_id=test_vendor.id,
-            marketplace_product_id=test_marketplace_product.id,
-        )
-        db.add(product)
-        db.commit()
-        db.refresh(product)
-
-        # Should inherit from marketplace product
-        assert product.effective_price == 100.00
-        assert product.effective_brand == "SourceBrand"
-
-        # Now override the price
-        product.price = 89.99
-        db.commit()
-        db.refresh(product)
-
-        # Should use the override
-        assert product.effective_price == 89.99
-        # Brand still inherited
-        assert product.effective_brand == "SourceBrand"
-
-    def test_product_reset_to_source(self, db, test_vendor, test_marketplace_product):
-        """Test reset_to_source methods."""
-        # Set up marketplace product values (use cents internally)
+        Products are independent entities with all fields populated at creation.
+        Source values are kept for comparison only, not inheritance.
+        """
+        # Set up marketplace product values
         test_marketplace_product.price_cents = 10000  # €100.00
         test_marketplace_product.brand = "SourceBrand"
         db.commit()
 
-        # Create product with overrides (price property converts euros to cents)
+        # Create product with its own values (independent copy pattern)
         product = Product(
             vendor_id=test_vendor.id,
             marketplace_product_id=test_marketplace_product.id,
-            price_cents=8999,  # €89.99
-            brand="OverrideBrand",
+            price_cents=8999,  # €89.99 - vendor's price
+            brand="VendorBrand",  # Vendor's brand
         )
         db.add(product)
         db.commit()
         db.refresh(product)
 
-        assert product.effective_price == 89.99
-        assert product.effective_brand == "OverrideBrand"
+        info = product.get_source_comparison_info()
 
-        # Reset price_cents to source (OVERRIDABLE_FIELDS now uses _cents names)
-        product.reset_field_to_source("price_cents")
-        db.commit()
-        db.refresh(product)
+        # Product has its own price
+        assert info["price"] == 89.99
+        assert info["price_cents"] == 8999
+        assert info["price_source"] == 100.00  # Original marketplace price
 
-        assert product.price_cents is None
-        assert product.price is None  # Property returns None when cents is None
-        assert product.effective_price == 100.00  # Now inherits from marketplace
+        # Product has its own brand
+        assert info["brand"] == "VendorBrand"
+        assert info["brand_source"] == "SourceBrand"  # Original marketplace brand
 
-        # Reset all fields
-        product.reset_all_to_source()
-        db.commit()
-        db.refresh(product)
+        # No more *_overridden keys in the pattern
+        assert "price_overridden" not in info
+        assert "brand_overridden" not in info
 
-        assert product.brand is None
-        assert product.effective_brand == "SourceBrand"  # Now inherits
+    def test_product_fields_are_independent(
+        self, db, test_vendor, test_marketplace_product
+    ):
+        """Test that product fields don't inherit from marketplace product.
 
-    def test_product_get_override_info(self, db, test_vendor, test_marketplace_product):
-        """Test get_override_info method."""
-        test_marketplace_product.price_numeric = 100.00
+        Products are independent entities - NULL fields stay NULL,
+        no inheritance/fallback logic.
+        """
+        # Set up marketplace product values
+        test_marketplace_product.price_cents = 10000
         test_marketplace_product.brand = "SourceBrand"
         db.commit()
 
+        # Create product without copying values
         product = Product(
             vendor_id=test_vendor.id,
             marketplace_product_id=test_marketplace_product.id,
-            price=89.99,  # Override
-            # brand not set - will inherit
+            # Not copying price_cents or brand
         )
         db.add(product)
         db.commit()
         db.refresh(product)
 
-        info = product.get_override_info()
+        # Fields should be NULL (not inherited)
+        assert product.price_cents is None
+        assert product.price is None
+        assert product.brand is None
 
-        # Price is overridden
-        assert info["price"] == 89.99
-        assert info["price_overridden"] is True
+        # But we can still see the source values for comparison
+        info = product.get_source_comparison_info()
         assert info["price_source"] == 100.00
-
-        # Brand is inherited
-        assert info["brand"] == "SourceBrand"
-        assert info["brand_overridden"] is False
         assert info["brand_source"] == "SourceBrand"