VS Code plugin: after "Clear URL", the Hub status bar still says "Click to reconnect" #3523

Bug Report

Steps to Reproduce:

1. Connect the VS Code plugin to a CALM Hub URL that does not respond. The status bar shows "CALM Hub (error)".
2. Click the CALM Hub status bar item and select "Clear URL".
3. Hover over the status bar item, then click it.

Expected Result:

The tooltip says "Click to connect to CalmHub", and the click opens an empty URL box.

Actual Result:

The tooltip says "Disconnected from " and "Click to reconnect", but the click opens an empty URL box. "Clear URL" clears calm.hub.url, but HubStatusBar keeps the old URL: setState changes hubUrl only when it gets a value (calm-plugins/vscode/src/extension/services/hub-status-bar.ts:32-34).

Environment:

VS Code plugin at 70866e6 (main).

Additional Context:

Found in the review of #3516, which fixes #3494 for "Disconnect". Let HubStatusBar forget the URL when "Clear URL" runs, so that the tooltip and the next click agree.