The sentinel closes its own shared-red issue when the test passes again with no fix, instead of handing it to a builder #8287

A shared red often ends by itself: main's next green check, or a base that moved on. #8259 and #8275 still went to builders, who found nothing to fix and declined twice. That is red noise on the owner's board.

Done when:

• [ ] When a shared: span has closed, no pull has failed the test since then (pullsFailedSince), and main's newest check is green on it, the sentinel comments "passed again on its own at <time>; evidence: …" and closes its own open issue for that cause as dropped, before any builder is given it
• [ ] An issue a person has commented on is never closed this way
• [ ] If the same cause opens again within a day, the sentinel reopens the work as a fresh issue that quotes the earlier one, as stillDegraded does
• [ ] test/sentinel-shared-settle.test.ts proves the close, the person's-comment exception and the fresh issue on a repeat. It fails without the change

Files: src/crew/sentinel.ts, test/sentinel-shared-settle.test.ts Risk: a real flake that fails rarely closes and comes back. The repeat rule keeps it from disappearing.