Add live dashboard streaming and UI updates

[Xento]

Summary

• add a dashboard streaming endpoint plus JSON API that reuse cached AMS data
• broadcast MQTT-driven AMS updates to connected clients with versioned change detection
• update the home page to subscribe to the stream, re-render trays in the browser, and show connection status with a fallback poller

Testing

• python -m compileall app.py mqtt_bambulab.py

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Codex Task