Add bounty payout eligibility gate

[SIRXIII]

/claim #18

Summary

• Adds bounty-payout-eligibility-gate, a dependency-free payout readiness module for Scientific Bounty System settlement review.
• Checks contributor identity attestation, supported payout country, payout method, tax form, institution routing, watchlist status, award splits, sponsor funding, and IP release guardrails.
• Produces contributor payout plans, sponsor remediation actions, and deterministic SHA-256 audit packets from synthetic data only.

Demo

• Short H.264 demo artifact included at bounty-payout-eligibility-gate/docs/demo.mp4.

Validation

• npm run check
• npm test
• npm run demo
• ffprobe -v error -select_streams v:0 -show_entries stream=codec_name,width,height,duration -of default=noprint_wrappers=1 docs/demo.mp4
• git diff --check
• rg -n "api[_-]?key|private[_-]?key|password|secret|token|wallet|ssn" bounty-payout-eligibility-gate || true

AI-assisted with OpenAI Codex; I reviewed and verified the diff locally before submitting.