A failed check's one-line summary names up to three failing tests and how many more, not only the first #6271

src/checks/summary.ts puts only detail.names[0] in the summary. When #6076 was parked, the reason read "flow vitals > …" twice. The test its branch really broke, apps-door's phase lists, was third in checkDetail.names, and nobody reading the summary saw it.

Done when:

• [ ] summariseCheckFailure writes N of T tests — "a", "b", "c" and K more with at most three distinct names, still truncated by truncate as today. With one failure, it reads exactly as it does now.
• [ ] The park comment and the pull's check line read that summary unchanged. No other caller has to change.
• [ ] Tests cover one name, three names, and five names ("and 2 more"), plus a name list longer than the truncation limit.

Files: src/checks/summary.ts, its test. Risk: other code may match the old summary text. Grep for tests — and update any parser in the same pull.