Clean stale active-ci-watch.env (points at merged #11191; should reflect no active watch)

Per LEARNINGS 2026-05-29 04:10 UTC Action Item #4. active-ci-watch.env still says STATUS=green for #11191 even though #11191 merged. Not actively dangerous but appears in 3 consecutive reflections as stale. DoD: (a) gh pr view 11191 to confirm merged; (b) update active-ci-watch.env header LAST_VERIFIED to current UTC; (c) clear PR_NUMBERS or set STATUS=none and PR_NUMBERS= to reflect no active watch; (d) commit or leave uncommitted as the file is workspace-local; (e) PATCH this task to completed with result.summary describing the change.