feat: add session-owned worktree cleanup audit and TTL enforcement (Closes #401)

Stale worktrees accumulate under branches/ when runs stop early, race a
sibling session, hit a validation failure, or lose cwd state, making later
workflow decisions harder and riskier.

Changes:
- worktree_cleanup_audit.py — ownership metadata, safety-first classifier
  (active_open_pr, active_issue_work, dirty_local_worktree,
  clean_stale_removable, detached_review_leftover, unsafe_unknown), TTL
  expiry, per-worktree removal proof, and success-completion cleanup plan.
  Only clean_stale_removable and detached_review_leftover are removable;
  dirty/PR/leased/protected/unknown worktrees are never auto-deleted.
- gitea_audit_worktree_cleanup — read-only MCP tool that classifies every
  branches/ entry, fetches live open-PR heads (fails closed if unavailable),
  and returns counts, removable candidates, and git worktree list proof.
- work-issue.md 22A + review-merge-pr.md 28 — cleanup/TTL workflow rules.
- tests/test_worktree_cleanup_audit.py — 30 cases covering all nine
  acceptance scenarios plus inference, metadata, TTL, and report accuracy.

Validation:
  /Users/jasonwalker/Development/Gitea-Tools/venv/bin/python \
    -m unittest tests.test_worktree_cleanup_audit tests.test_merged_cleanup_reconcile -q
  38 passed.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

skills/llm-project-workflow/workflows/work-issue.md

@@ -691,6 +691,39 @@ Do not update the main checkout unless the canonical workflow explicitly allows
 
 Any cleanup is a mutation and must be reported.
 
+### 22A. Session-owned worktree cleanup and TTL (#401)
+
+Every session-owned worktree created under `branches/` has ownership metadata:
+path, workflow type, issue number, PR number, branch/head SHA, creator
+identity/profile, created timestamp, last-used timestamp, and cleanup
+eligibility.
+
+Cleanup is classification-driven. `gitea_audit_worktree_cleanup` (read-only)
+classifies every `branches/` entry as exactly one of:
+
+* `active_open_pr` — branch has an open PR; never auto-removed.
+* `active_issue_work` — active claim/lease or fresh issue worktree; never
+  auto-removed.
+* `dirty_local_worktree` — uncommitted changes; never auto-removed.
+* `clean_stale_removable` — clean, no PR, no lease; removable.
+* `detached_review_leftover` — clean detached review/baseline/merge-simulation
+  worktree; removable.
+* `unsafe_unknown` — protected base checkout or unknown workflow type; never
+  auto-removed.
+
+Only `clean_stale_removable` and `detached_review_leftover` may be removed, and
+only one-by-one after `git worktree list` proof plus per-worktree proof of:
+worktree path, branch/HEAD, clean/dirty status, no active PR/lease, and the
+removal result. Review, baseline, and merge-simulation worktrees are removed
+automatically at successful workflow completion; issue/conflict-fix worktrees
+are removed only after their TTL (`GITEA_WORKTREE_TTL_HOURS`, default 24h)
+expires and no lock/lease is held.
+
+Dirty, active-PR, active-issue, and leased worktrees are never deleted
+automatically. If a removal fails, the final report must list the leftover
+worktree path and the reason. Include the `git worktree list` output as final
+cleanup verification.
+
 ## 23. Recovery handoff rules
 
 If blocked, produce a recovery handoff with: