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>
