Expose printer telemetry at /api/v1/metrics in Prometheus text format for
integration with Grafana, Prometheus, and other monitoring systems.
Backend:
- Add metrics.py route with GET /api/v1/metrics endpoint
- Support optional bearer token authentication
- Export printer metrics: connection, state, temperatures, fans, WiFi
- Export print metrics: progress, remaining time, layer count
- Export statistics: prints by status, filament used, print time
- Export queue metrics: pending and active jobs
- Add prometheus_enabled and prometheus_token settings
Frontend:
- Add Prometheus Metrics card in Settings → Network tab
- Toggle to enable/disable metrics endpoint
- Optional bearer token field for authentication
- Display list of available metrics
Tests:
- Add test_metrics_api.py with 7 integration tests
- Test access control (disabled, enabled, token auth)
- Test metrics format and content validation
