Get chat status

Whether the agent is ready for chat, for a caller its web chat access admits. Needs account membership, not a role on the agent, so a caller who may only chat can tell whether the agent is running. Returns the coarse status and whether the messaging sidecar is reachable, without the details GET /deployments/{deploymentId}/status carries. A caller the web chat access refuses, an agent in another account, a deleted agent, or one without web chat gets 404, as for an unknown deployment.