Write wiki page for the YAML frontmatter body integrity protection system.

Cover:

• Root cause: fix-broken-yaml.py stripped block scalars (body:|) continuation lines
• lib/body-integrity.ts — post-write verification, re-reads file after write
• verifyBodyIntegrity() in 4 critical paths: delegateTask, updateTaskFields, dismissReview, requestReview
• scripts/validate-yaml-frontmatter.ts — comprehensive validator
• Pre-commit hook at .git/hooks/pre-commit — blocks commits with broken frontmatter
• 4 body-survival tests in tests/actions-core.test.ts
• Rules: always check duplicate keys before writing, quote colon-titled titles
• See: lib/body-integrity.ts, lib/actions.ts, scripts/validate-yaml-frontmatter.ts, .git/hooks/pre-commit