Require and validate Controller Handoff sections in workflow final reports

- Upgrade SKILL.md §K compact format to the issue #182 canonical field set
  (Task/Repo/Role/Identity/Issue-PR/Branch-SHA/Files/Validation/Mutations/
  Current status/Blockers/Next/Safety) plus role-specific field lists for
  review/merge, author, and queue/inventory tasks.
- Point the review-pr, merge-pr, and start-issue template handoff lines at
  the exactly-titled Controller Handoff section with their role fields.
- Add review_proofs.assess_controller_handoff(): reports without the exact
  section are 'missing' (downgraded), present-but-partial are 'incomplete'
  with the absent fields listed, and role extras are enforced per role.
- Add TestControllerHandoff (8 tests) including a SKILL.md doc-contract
  test so the documented requirement cannot silently rot.

The handoff supplements the full report; full-report validation rules are
unchanged.

Closes #182

Co-Authored-By: Claude Fable 5 <[email protected]>

skills/llm-project-workflow/templates/merge-pr.md

@@ -35,5 +35,11 @@ Then run the cleanup template (worktree-cleanup.md):
 - delete remote branch, remove local branch + worktree folder
 - fetch/prune; confirm main checkout is clean and current (0 0).
 
-Handoff: reviewer identity, merge result + commit, cleanup done, issue closed, PR metadata state/merged flag/hash, remote master hash, post-merge verification method used & verification results.
+Handoff: end with a section titled exactly `Controller Handoff` per SKILL.md
+§K (long form — a merge is always high-risk), including the review/merge role
+fields (Selected PR, Reviewer eligibility, Pinned reviewed head, Review
+decision, Merge result, Linked issue status, Cleanup status) plus: merge
+commit, PR metadata state/merged flag/hash, remote master hash, and the
+post-merge verification method used & verification results. Reports missing
+the handoff are downgraded (review_proofs.assess_controller_handoff).
 ```