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/src/app.module.ts

@@ -2,10 +2,12 @@ import { Module } from '@nestjs/common';
 import { AppController } from './app.controller';
 import { AppService } from './app.service';
 import { StatusController } from './status.controller';
+import { DeviceEventsController } from './device-events.controller';
+import { DeviceDataService } from './device-data.service';
 
 @Module({
   imports: [],
-  controllers: [AppController, StatusController],
-  providers: [AppService],
+  controllers: [AppController, StatusController, DeviceEventsController],
+  providers: [AppService, DeviceDataService],
 })
 export class AppModule {}