feat: add Z-Wave network scan via MQTT gateway

Import a Z-Wave JS UI (zwavejs2mqtt) network over the MQTT gateway API,
mirroring the existing Zigbee pipeline:

- New Z-Wave Import modal + sidebar entry (broker, prefix, gateway name)
- coordinator/router/end-device typing with mesh tree from node neighbors
- import to Pending section or straight to canvas
- Pending Devices gains a Z-Wave source filter
- shared mqtt_common helpers extracted from the zigbee service

ha-relevant: yes

backend/app/main.py

@@ -7,7 +7,7 @@ from typing import Any
 from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
 
-from app.api.routes import auth, canvas, designs, edges, liveview, nodes, scan, stats, status, zigbee
+from app.api.routes import auth, canvas, designs, edges, liveview, nodes, scan, stats, status, zigbee, zwave
 from app.api.routes import settings as settings_routes
 from app.core.config import settings
 from app.core.scheduler import start_scheduler, stop_scheduler
@@ -57,6 +57,7 @@ app.include_router(status.router, prefix="/api/v1/status", tags=["status"])
 app.include_router(settings_routes.router, prefix="/api/v1/settings", tags=["settings"])
 app.include_router(liveview.router, prefix="/api/v1/liveview", tags=["liveview"])
 app.include_router(zigbee.router, prefix="/api/v1/zigbee", tags=["zigbee"])
+app.include_router(zwave.router, prefix="/api/v1/zwave", tags=["zwave"])
 app.include_router(stats.router, prefix="/api/v1/stats", tags=["stats"])