feat: add Zigbee2MQTT network map importer

- Backend: async MQTT service (aiomqtt) to fetch Z2M networkmap via bridge API
- Backend: FastAPI router at /api/v1/zigbee with /import and /test-connection
- Backend: Pydantic v2 schemas for request/response validation
- Backend: coordinator → router → end-device parent_id hierarchy builder
- Frontend: ZigbeeImportModal with MQTT config form, Test Connection, Fetch Devices
- Frontend: device list grouped by type (coordinator/router/enddevice) with checkboxes
- Frontend: ZigbeeCoordinatorNode, ZigbeeRouterNode, ZigbeeEndDeviceNode canvas nodes
- Frontend: Zigbee Import button in sidebar alongside Scan Network
- Frontend: handleZigbeeAddToCanvas wires selected devices + edges onto canvas
- Tests: full unit test suite for parser, hierarchy builder, MQTT mocks
- Tests: API endpoint tests for /zigbee/import and /zigbee/test-connection
- Tests: Vitest component tests for ZigbeeImportModal
- Docs: docs/zigbee-import.md with full usage, MQTT config, troubleshooting guide
- Docs: README.md Zigbee2MQTT Import section

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

backend/requirements.txt

@@ -17,6 +17,7 @@ types-PyYAML==6.0.12.20240917
 websockets==13.1
 httpx==0.27.2
 zeroconf==0.131.0
+aiomqtt==2.3.0
 
 # Dev
 ruff==0.6.9