raise_for_status raises httpx's own HTTPStatusError, whose message stops at the
status line and the URL. FastAPI's {"detail": ...} — the half that says what to
do about it — was dropped, so every rejection reached the calling AI as a bare
"Client error '422 Unprocessable Content'" with nothing to act on.
Replaces it with a BackendError naming the method, path, status and detail.
A structured detail (the approve-duplicate prompt answers with an object) is
serialized rather than lost, a non-JSON body falls back to its text, and the
whole thing is capped so an HTML error page can't land in the client's context.
ha-relevant: no
Pouzor
71e78b4279