Add repository retention legal hold gate

[haki203]

Summary

• add a self-contained repository retention and legal-hold gate for issue Project Repository & Version Control #10
• evaluate tagged repository releases and destructive export actions against active legal holds, archive evidence, component hashes, and export bundle manifest hashes
• generate deterministic reviewer artifacts: JSON decision packet, Markdown report, SVG summary, and short MP4 demo video

Safety

• synthetic sample data only
• no real repositories, secrets, tokens, patient data, private dashboard data, payout details, or external service calls

Demo

• repository-retention-legal-hold-gate/reports/demo.mp4

Validation

• node repository-retention-legal-hold-gate/test.js
• node repository-retention-legal-hold-gate/demo.js
• node --check repository-retention-legal-hold-gate/index.js
• node --check repository-retention-legal-hold-gate/sample-data.js
• node --check repository-retention-legal-hold-gate/demo.js
• git diff --check
• ffmpeg decode check: ffmpeg -v error -i repository-retention-legal-hold-gate/reports/demo.mp4 -f null -

/claim #10