cluster_status on a removed node should clearly indicate removal and close sockets

## Problem

After a node is removed from a cluster, calling `cluster_status` on that node still shows `database_sockets` with `connected: false`, with no indication that the node is no longer an active cluster member. This is confusing — the sockets should be closed and the status should clearly state the node has been removed.

## Proposed

- Add a top-level field indicating the node is not part of any active cluster
- Close the stale socket entries on removal (currently they're only closed after a restart)

🤖 Filed by Claude on behalf of Kris.