curl --request GET \
  --url https://api.topcalls.ai/v1/voices/builtin \
  --header 'Authorization: Bearer <token>'

{
  "realtime": {
    "provider": "<string>",
    "voices": [
      {
        "name": "<string>",
        "description": "<string>",
        "provider": "<string>",
        "mode": "<string>",
        "language": "<string>",
        "gender": "<string>"
      }
    ],
    "default": "<string>"
  },
  "legacy": {
    "elevenlabs": {
      "voices": [
        {
          "name": "<string>",
          "id": "<string>",
          "description": "<string>",
          "provider": "<string>",
          "gender": "<string>",
          "age": "<string>"
        }
      ],
      "default_id": "<string>"
    },
    "deepgram": {
      "voices": [
        {
          "name": "<string>",
          "description": "<string>",
          "provider": "<string>",
          "language": "<string>",
          "gender": "<string>"
        }
      ],
      "default": "<string>"
    }
  }
}