Add Grafana lint gate and refresh observability docs

[MontrealAI]

Summary

• add a docker/fallback Grafana dashboard lint script and expose it via npm scripts
• enforce the Grafana dashboard lint gate in CI and required checks, and refresh badges/readme guidance
• update DCUtR dashboard documentation to point to the new lint entrypoint

Testing

• npm run grafana:lint
• npm run test
• npm run test:frontend
• npm run lint:md

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Codex Task

[chatgpt-codex-connector]

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