feat: add MQTT integration for real-time entity updates

- aiomqtt async client with auto-reconnect and topic store
- MQTT router: GET /api/mqtt, GET /api/mqtt/topic/{path}, POST /api/mqtt/publish
- MQTT entities included in /api/all + WebSocket broadcast
- MqttCard frontend component with category filters, entity list
- Configurable via ENV: MQTT_HOST, MQTT_PORT, MQTT_USERNAME,
  MQTT_PASSWORD, MQTT_TOPICS (comma-separated or JSON array)
- Gracefully disabled when MQTT_HOST is not set

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/main.py

@@ -12,6 +12,7 @@ from fastapi.staticfiles import StaticFiles
 
 from server.config import settings
 from server.services import news_service
+from server.services.mqtt_service import mqtt_service
 
 logger = logging.getLogger("daily-briefing")
 logging.basicConfig(
@@ -42,10 +43,28 @@ async def lifespan(app: FastAPI):
     except Exception:
         logger.exception("Failed to initialize database pool — news will be unavailable")
 
+    # Start MQTT service
+    if settings.mqtt_host:
+        try:
+            await mqtt_service.start(
+                host=settings.mqtt_host,
+                port=settings.mqtt_port,
+                username=settings.mqtt_username or None,
+                password=settings.mqtt_password or None,
+                topics=settings.mqtt_topics,
+                client_id=settings.mqtt_client_id,
+            )
+            logger.info("MQTT service started (broker %s:%d)", settings.mqtt_host, settings.mqtt_port)
+        except Exception:
+            logger.exception("Failed to start MQTT service — MQTT will be unavailable")
+    else:
+        logger.info("MQTT disabled — set MQTT_HOST to enable")
+
     yield
 
     # Shutdown
     logger.info("Shutting down...")
+    await mqtt_service.stop()
     await news_service.close_pool()
 
 
@@ -65,13 +84,14 @@ app.add_middleware(
 )
 
 # --- Register Routers ---
-from server.routers import dashboard, homeassistant, news, servers, tasks, weather  # noqa: E402
+from server.routers import dashboard, homeassistant, mqtt, news, servers, tasks, weather  # noqa: E402
 
 app.include_router(weather.router)
 app.include_router(news.router)
 app.include_router(servers.router)
 app.include_router(homeassistant.router)
 app.include_router(tasks.router)
+app.include_router(mqtt.router)
 app.include_router(dashboard.router)
 
 # --- Serve static frontend (production) ---