fix: adhere to CONTRIBUTING.md — ruff clean + all tests passing

- Move aiomqtt to module-level import (enables proper patch() in tests)
- Remove unused variable (description) in zigbee_service — ruff F841
- Split long line (132 chars) to fit 120 char limit — ruff E501
- Fix import sort order in test files — ruff I001
- Remove unused imports (asyncio, AsyncMock, MagicMock) — ruff F401
- Rename test_mqtt_connection import alias to _test_mqtt_connection
  to avoid pytest fixture name collision (ERROR at setup)
- All 33 backend tests now pass (21 service + 12 router)
- TypeScript typecheck: 0 errors

Co-authored-by: CyberKeys <noreply@openclaw.ai>

backend/tests/test_zigbee_service.py

@@ -2,11 +2,11 @@
 
 from __future__ import annotations
 
-import asyncio
 import json
 from typing import Any
-from unittest.mock import AsyncMock, MagicMock, patch
+from unittest.mock import patch
 
+import aiomqtt  # noqa: F401
 import pytest
 
 from app.services.zigbee_service import (
@@ -14,9 +14,10 @@ from app.services.zigbee_service import (
     _z2m_type_to_homelable,
     fetch_networkmap,
     parse_networkmap,
-    test_mqtt_connection,
 )
-
+from app.services.zigbee_service import (
+    test_mqtt_connection as _test_mqtt_connection,
+)
 
 # ---------------------------------------------------------------------------
 # Helper builders
@@ -341,7 +342,7 @@ async def test_test_mqtt_connection_success() -> None:
         mock_aiomqtt.Client.return_value = _FakeClient()
         mock_aiomqtt.MqttError = Exception
 
-        result = await test_mqtt_connection("localhost", 1883)
+        result = await _test_mqtt_connection("localhost", 1883)
     assert result is True
 
 
@@ -359,4 +360,4 @@ async def test_test_mqtt_connection_failure() -> None:
         mock_aiomqtt.MqttError = Exception
 
         with pytest.raises(ConnectionError):
-            await test_mqtt_connection("bad-host", 1883)
+            await _test_mqtt_connection("bad-host", 1883)