[codex] Add reputation transparency receipts

[newmattock]

Addresses #15

Summary

• add reputation-transparency-receipts, a focused reputation transparency slice for issue Community & User Reputation System #15
• generate privacy-preserving visibility receipts for reviews and contributions, contributor reputation reports, moderation findings, and a deterministic evidence digest
• include sample community input, requirement map, SVG walkthrough, and short MP4 demo

Validation

Fresh validation on 2026-05-17 21:04 PDT:

• npm run check
• npm test -> Node test runner passed 4 tests, 0 failures
• npm run demo -> evidence digest 99c1a769f15c7b44, 2 review receipts, 3 contribution receipts, 2 moderation findings, and leaderboard output
• file docs/demo.mp4 docs/demo.svg -> MP4 v2 and SVG
• git diff --check
• focused sensitive-string scan for API keys, secrets, tokens, passwords, private keys, wallet material, and EVM addresses

/claim #15