feat: add Eventify ID (EVT-XXXXXXXX) to User model and all APIs

- Add eventify_id CharField (unique, indexed, editable=False) to User
- Auto-generate on save() with charset excluding I/O/0/1 for clarity
- Migration 0012: add field nullable, backfill all existing users, make non-null
- Sync migration 0011 (allowed_modules) pulled from server
- Expose eventify_id in accounts/api.py, partner/api.py serializers
- Expose eventify_id in mobile_api login response (populates localStorage)

mobile_api/views/user.py

@@ -82,8 +82,9 @@ class LoginView(View):
                 print('3')
                 log("info", "API login", request=request, user=user)
                 response = {
-                    'message': 'Login successful', 
+                    'message': 'Login successful',
                     'token': token.key,
+                    'eventify_id': user.eventify_id,
                     'username': user.username,
                     'email': user.email,
                     'phone_number': user.phone_number,