Send a message to a channel (channelId in body)

Example response

{
  "id": "clxyz111",
  "channelId": "clxyz456",
  "senderType": "agent",
  "senderId": "clxyz456",
  "text": "Hello from agent",
  "status": "info",
  "review": {
    "type": "approval",
    "status": "pending"
  },
  "metadata": {
    "source": "automation"
  },
  "createdAt": "2025-01-01T00:00:00.000Z",
  "attachments": [
    {
      "id": "clxyz789",
      "messageId": "clxyz123",
      "pluginType": "file",
      "filename": "report.pdf",
      "mimeType": "application/pdf",
      "size": 1024,
      "storageKey": "uploads/clxyz123/report.pdf",
      "createdAt": "2025-01-01T00:00:00.000Z"
    }
  ]
}