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/__init__.py

@@ -1,17 +1,16 @@
 # models/__init__.py
 """Models package - Database and API models."""
 
-# Database models (SQLAlchemy)
-from .database.base import Base
-from .database.user import User
-from .database.marketplace_product import MarketplaceProduct
-from .database.inventory import Inventory
-from .database.vendor import Vendor
-from .database.product import Product
-from .database.marketplace_import_job import MarketplaceImportJob
-
 # API models (Pydantic) - import the modules, not all classes
 from . import schema
+# Database models (SQLAlchemy)
+from .database.base import Base
+from .database.inventory import Inventory
+from .database.marketplace_import_job import MarketplaceImportJob
+from .database.marketplace_product import MarketplaceProduct
+from .database.product import Product
+from .database.user import User
+from .database.vendor import Vendor
 
 # Export database models for Alembic
 __all__ = [