Add collaborative section lock arbiter

[vondutchi]

/claim #12

Summary

• Add collaborative-section-lock-arbiter/, a distinct real-time editor slice for controlled-section lock arbitration.
• Evaluate requested edits against lock ownership, stale presence heartbeats, final-figure/data freeze windows, pending suggestions, and reviewer override eligibility.
• Emit deterministic reviewer artifacts in JSON, Markdown, SVG, and MP4 form using synthetic data only.

Scope Boundaries

This is synthetic demo data only. It does not call external editors, notebook kernels, identity providers, storage services, payment systems, live documents, private project data, credentials, or tokens.

This scope is intentionally separate from existing #12 slices such as full editor implementations, notebook execution, autosave/version history, citation/reference tooling, task workflow, chat/sidebar, broad presence indicators, or generic collaboration dashboards.

Demo

• collaborative-section-lock-arbiter/reports/demo.mp4

Validation

• node collaborative-section-lock-arbiter/test.js
• node collaborative-section-lock-arbiter/demo.js
• node collaborative-section-lock-arbiter/render-video.js
• ffprobe confirmed H.264, 960x540, 5 seconds, 120 frames for the demo MP4.
• node --check collaborative-section-lock-arbiter/index.js
• node --check collaborative-section-lock-arbiter/sample-data.js
• node --check collaborative-section-lock-arbiter/test.js
• node --check collaborative-section-lock-arbiter/demo.js
• node --check collaborative-section-lock-arbiter/render-video.js
• git diff --cached --check

No payout details, secrets, tokens, cookies, or private account information are included in this PR.