--device nvidia on a machine without one reported "no usable backend remains",
which says nothing about the cause and repeated the same message once per URL.
Asking for a device that cannot run is a configuration mistake, so it now fails
once, fatally, naming the reason: "nvidia/cuda: no nvidia hardware detected".
Found by end-to-end testing; the unit tests only covered the runtime-failure
path, where TranscribeError remains correct.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>