Text to speech
POST /v1/audio/speech takes a JSON body and returns audio bytes.
Transcription
POST /v1/audio/transcriptions is multipart/form-data with a file part and a model field.
SPEECH_MODEL and TRANSCRIBE_MODEL to ids from the catalog. Available voices, formats, and other fields depend on the model; check its catalog row. Both calls return the usual x-predev-* headers and are billed from usage.cost.
