SseMessage

Payload do data de cada event: message no stream SSE. Só mensagens outbound
(atendente, IA ou sistema) trafegam por aqui.

{
    "uuid": "095be615-a8ad-4c33-8e9c-c7612fbf6c9f",
    "type": "text",
    "text": "string",
    "media_url": "string",
    "media_name": "string",
    "media_mime": "string",
    "timestamp": "2019-08-24T14:15:22.123Z"
}