Merge pull request #3863 from hathach/claude/validate-loop

validate workflow: loop validate -> fix cycles until green

Turn the single-pass validate gate into a loop: run unit + builds +
size + PVS + claude/codex reviews in parallel; on a red verdict one
fix agent repairs the gate-failing evidence (CONFIRMED findings,
codex P0/P1, failed stages - PLAUSIBLE/quality stay report-only),
commits, and the affected stages re-run, up to maxCycles (default 5).

Hardened per review: fix-commit paths verified from git rather than
self-report, restartRequired when a fix edits the workflow itself,
per-stage evidence budgeting so the fixer prompt JSON never truncates
mid-document, dirty-tree and moving-base-ref guards, dead stage
agents retried instead of ending the loop, and only pure-docs fixes
skip a full stage re-run.