Refactor to manager-centric model, add team calendar for all users

Key changes:
- Removed office-centric model (deleted offices.py, office-rules)
- Renamed to team-rules, managers are part of their own team
- Team calendar visible to all (read-only for employees)
- Admins can have a manager assigned

services/notifications.py

@@ -21,7 +21,7 @@ import uuid
 
 from database.models import (
     User, UserPresence, DailyParkingAssignment,
-    NotificationLog, NotificationQueue, OfficeMembership
+    NotificationLog, NotificationQueue
 )
 from services.parking import get_spot_display_name