feat(08-04): create backend/api/admin/ package — users, quotas, ai, shared, init
- users.py: list_users, create_user, update_user_status, initiate_password_reset,
update_ai_config, delete_user, create_system_topic (7 routes)
- quotas.py: get_user_quota, update_user_quota (2 routes)
- ai.py: get_ai_config_models, test_ai_connection, get_ai_config,
update_system_ai_config (4 routes); validate_provider_id call-through (D-11)
- shared.py: _user_to_dict helper (T-02-27 / SEC-07 field whitelist)
- __init__.py: router aggregator with prefix=/api/admin; 13 routes total
- admin.py monolith renamed to admin_OLD_REMOVE_IN_TASK_3.py (deleted in task 3)
- All sub-routers have NO prefix (D-04)
- All handlers inject Depends(get_current_admin) (T-08-04-01)
curo1305
3ec198768d