- 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
- Create Availability model with date, start_time, end_time
- Add availability schemas with 15-minute boundary validation
- Add admin endpoints:
- GET /api/admin/availability - query by date range
- PUT /api/admin/availability - set slots for a date
- POST /api/admin/availability/copy - copy to multiple days
- Add 26 tests covering permissions, CRUD, and validation