- Add ruff as dev dependency
- Configure ruff in pyproject.toml with strict 88-char line limit
- Ignore B008 (FastAPI Depends pattern is standard)
- Allow longer lines in tests for readability
- Fix all lint issues in source files
- Add Makefile targets: lint-backend, format-backend, fix-backend
- Replaced all UTC imports with timezone imports
- Changed all datetime.now(UTC) to datetime.now(timezone.utc)
- Consistent with booking.py and more explicit about timezone usage
- Updated models.py, routes/auth.py, and routes/invites.py