repo mirror detach: report an ambiguous real call and an unread stall

A real detach that got no answer, a 5xx, or an interruption may still have frozen and rewired the repo, and the /gh/ ref may already answer moved, so print the entire api follow-up there too; only a 4xx proves nothing changed.

A stall reported without a state read (--no-wait) no longer promises the server's sweep resumes it: only GET /repos/{repoId}/detach says whether it is resumable.

Lock the RepoDetachState.status loosening with its own client test.