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>

docker-compose.yml

@@ -22,6 +22,12 @@ services:
       - VIKUNJA_TOKEN=${VIKUNJA_TOKEN}
       # Unraid Servers (JSON array)
       - UNRAID_SERVERS=${UNRAID_SERVERS:-[]}
+      # MQTT (optional)
+      - MQTT_HOST=${MQTT_HOST:-}
+      - MQTT_PORT=${MQTT_PORT:-1883}
+      - MQTT_USERNAME=${MQTT_USERNAME:-}
+      - MQTT_PASSWORD=${MQTT_PASSWORD:-}
+      - MQTT_TOPICS=${MQTT_TOPICS:-#}
     extra_hosts:
       - "host.docker.internal:host-gateway"
     restart: always