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

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Change detection always dirty after dashboard render

The new change-detection guard compares incoming MQTT vt_tray/ams payloads to the cached LAST_AMS_CONFIG before bumping the dashboard version, but build_dashboard_payload mutates that same cache in place (see app.py lines 251‑264) by adding Spoolman enrichment fields. After any dashboard or /api/dashboard request, LAST_AMS_CONFIG no longer matches the raw telemetry, so this equality check always evaluates true and _increment_dashboard_version() fires on every MQTT report even when nothing changed. That means connected clients continuously rebuild the dashboard and refetch Spoolman data, generating unnecessary load and defeating the version gating intended here.

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