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

frontend/js/presence.js

@@ -10,9 +10,7 @@ let parkingData = {};
 let currentAssignmentId = null;
 
 document.addEventListener('DOMContentLoaded', async () => {
-    if (!api.requireAuth()) return;
-
-    currentUser = await api.getCurrentUser();
+    currentUser = await api.requireAuth();
     if (!currentUser) return;
 
     await Promise.all([loadPresences(), loadParkingAssignments()]);