refactor: modernize code quality tooling with Ruff

- Replace black, isort, and flake8 with Ruff (all-in-one linter and formatter)
- Add comprehensive pyproject.toml configuration
- Simplify Makefile code quality targets
- Configure exclusions for venv/.venv in pyproject.toml
- Auto-fix 1,359 linting issues across codebase

Benefits:
- Much faster builds (Ruff is written in Rust)
- Single tool replaces multiple tools
- More comprehensive rule set (UP, B, C4, SIM, PIE, RET, Q)
- All configuration centralized in pyproject.toml
- Better import sorting and formatting consistency

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

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

models/database/user.py

@@ -10,9 +10,10 @@ ROLE CLARIFICATION:
 - Vendor-specific roles (manager, staff, etc.) are stored in VendorUser.role
 - Customers are NOT in the User table - they use the Customer model
 """
+
 import enum
 
-from sqlalchemy import Boolean, Column, DateTime, Enum, Integer, String
+from sqlalchemy import Boolean, Column, DateTime, Integer, String
 from sqlalchemy.orm import relationship
 
 from app.core.database import Base