Harden stop-review gate sentinel parsing

[bbingz]

Summary

• add per-run stop-review sentinel tokens so echoed ALLOW/BLOCK lines from the previous Claude response cannot become the gate verdict
• update stop-review prompt instructions and add parser/runStopReview regressions
• extend the third-party review follow-up audit note, v0.6.21 draft notes, and changelog with the final cross-batch adjudication

Verification

• npm run build:plugins
• node --test plugins/polycli/scripts/tests/hooks.test.mjs packages/polycli-runtime/test/registry.test.js
• node --test plugins/polycli/scripts/tests/.test.mjs scripts/tests/.test.mjs
• node --test packages/polycli-utils/test/.test.js packages/polycli-runtime/test/.test.js packages/polycli-timing/test/*.test.js
• npm test
• git diff --check
• npm run release:check