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/schema/__init__.py

@@ -1,14 +1,9 @@
 # models/schema/__init__.py
 """API models package - Pydantic models for request/response validation."""
 
-from . import auth
 # Import API model modules
-from . import base
-from . import marketplace_import_job
-from . import marketplace_product
-from . import stats
-from . import inventory
-from . import vendor
+from . import (auth, base, inventory, marketplace_import_job,
+               marketplace_product, stats, vendor)
 # Common imports for convenience
 from .base import *  # Base Pydantic models