Rebase onto current prgs/master and fix cleanup-mutations regex so
"Cleanup mutations: none" does not false-positive the proof checklist.
Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>
Adds post_merge_cleanup_proof validation so cleanup claims must carry the
branch deletion and worktree removal checklists, or report CLEANUP_SKIPPED
with an exact blocker.
Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>