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/config.py

@@ -48,6 +48,14 @@ class Settings:
     news_cache_ttl: int = 300  # 5 min
     news_max_age_hours: int = 48
 
+    # --- MQTT ---
+    mqtt_host: str = ""
+    mqtt_port: int = 1883
+    mqtt_username: str = ""
+    mqtt_password: str = ""
+    mqtt_topics: List[str] = field(default_factory=lambda: ["#"])
+    mqtt_client_id: str = "daily-briefing"
+
     # --- Server ---
     host: str = "0.0.0.0"
     port: int = 8080
@@ -73,6 +81,20 @@ class Settings:
         s.vikunja_url = os.getenv("VIKUNJA_URL", s.vikunja_url)
         s.vikunja_token = os.getenv("VIKUNJA_TOKEN", s.vikunja_token)
 
+        s.mqtt_host = os.getenv("MQTT_HOST", s.mqtt_host)
+        s.mqtt_port = int(os.getenv("MQTT_PORT", str(s.mqtt_port)))
+        s.mqtt_username = os.getenv("MQTT_USERNAME", s.mqtt_username)
+        s.mqtt_password = os.getenv("MQTT_PASSWORD", s.mqtt_password)
+        s.mqtt_client_id = os.getenv("MQTT_CLIENT_ID", s.mqtt_client_id)
+
+        # Parse MQTT_TOPICS (comma-separated or JSON array)
+        raw_topics = os.getenv("MQTT_TOPICS", "")
+        if raw_topics:
+            try:
+                s.mqtt_topics = json.loads(raw_topics)
+            except (json.JSONDecodeError, TypeError):
+                s.mqtt_topics = [t.strip() for t in raw_topics.split(",") if t.strip()]
+
         s.debug = os.getenv("DEBUG", "").lower() in ("1", "true", "yes")
 
         # Parse UNRAID_SERVERS JSON