[codex] Add scientific bounty amendment control

Addresses #18

Summary

add scientific-bounty-amendment-control, a focused challenge/bounty amendment-control slice for issue #18
detect material sponsor changes after solver work starts, hold evaluation/payout readiness until affected teams receive notice and acknowledge, and generate deterministic audit evidence
include sample amendments, requirement map, SVG/MP4/GIF demo artifacts, and local validation scripts

Fresh validation on 2026-05-17 21:03 PDT:

npm run check
npm test -> Node test runner passed 4 tests, 0 failures
npm run demo -> digest b30b5da35d5e8a4a, 4 amendments reviewed, 4 material amendments, 2 critical findings, 1 high finding, 2 teams affected, evaluation decision hold, payout decision hold_until_acknowledged
npm run demo:gif -> wrote docs/demo.gif
file docs/demo.gif docs/demo.mp4 docs/demo.svg -> GIF image data, 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 #18