fix(trail): render every Core project error without the client dump

Review findings: a 500 still printed the generated client's error dump, and the 403 message read 'project not found: ... does not have access'. A small error type now renders 404, 403 and any other Core API status as one line (the server's detail plus status for the rest), matches its own sentinel, and still unwraps to the client error. 401 and non-API failures are unchanged.