Replace browser MQTT bridge with backend device-events service

The frontend previously connected directly to the MQTT broker via a
CDN-loaded Paho client and a Paho-specific ws proxy. Move that
responsibility into the backend: DeviceDataService persists MQTT
messages to Postgres, and DeviceEventsController exposes them over a
REST endpoint plus a WebSocket gateway that the frontend now consumes
directly. Also adds a pgadmin service for inspecting the database.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

backend/package.json

@@ -12,7 +12,14 @@
     "@nestjs/common": "^10.0.0",
     "@nestjs/core": "^10.0.0",
     "@nestjs/platform-express": "^10.0.0",
-    "reflect-metadata": "^0.1.13"
+    "@nestjs/platform-socket.io": "^10.0.0",
+    "@nestjs/websockets": "^10.0.0",
+    "@types/pg": "^8.20.0",
+    "mqtt": "^5.15.2",
+    "pg": "^8.22.0",
+    "reflect-metadata": "^0.1.13",
+    "rxjs": "^7.0.0",
+    "socket.io": "^4.7.0"
   },
   "devDependencies": {
     "@nestjs/cli": "^10.0.0",