hub-client: emit diagnostics when websockets fail

[cscheid]

We need better diagnostics for websocket connection issues, like Gordon is experiencing right now.

[gordonwoodhull]

To add context, this was probably a very long-running Firefox process. When I quit and restarted, it worked.

(It probably updated when I restarted, but according to Claude, it's more likely old WS connections jamming it up.)