curl --request POST \
  --url https://geoff.ai/api/v1/voice/upload-prompt \
  --header 'Authorization: Bearer <token>' \
  --form 'file=@prompt_audio.mp3'

{
  "data": {
    "file_id": "file_def456",
    "filename": "prompt_audio.mp3",
    "duration": 5.2,
    "format": "mp3"
  }
}