List Channel Bindings

curl -X GET https://api.app.shinzo.ai/v1/agent/a1b2c3d4-e5f6-7890-abcd-ef1234567890/channels \
  -H "Authorization: Bearer <token>"

{
  "bindings": [
    {
      "id": "bind_abc123",
      "channel": "api",
      "status": "active",
      "created_at": "2025-01-15T10:00:00Z"
    },
    {
      "id": "bind_def456",
      "channel": "discord",
      "status": "active",
      "discord_user_id": "123456789012345678",
      "discord_username": "myuser#1234",
      "created_at": "2025-01-16T12:00:00Z"
    }
  ]
}