style: apply black and isort formatting across entire codebase

- Standardize quote style (single to double quotes)
- Reorder and group imports alphabetically
- Fix line breaks and indentation for consistency
- Apply PEP 8 formatting standards

Also updated Makefile to exclude both venv and .venv from code quality checks.

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

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

models/database/marketplace_product.py

@@ -55,7 +55,9 @@ class MarketplaceProduct(Base, TimestampMixin):
     marketplace = Column(
         String, index=True, nullable=True, default="Letzshop"
     )  # Index for marketplace filtering
-    vendor_name = Column(String, index=True, nullable=True)  # Index for vendor filtering
+    vendor_name = Column(
+        String, index=True, nullable=True
+    )  # Index for vendor filtering
 
     product = relationship("Product", back_populates="marketplace_product")