[Feature Request] Add refreshInterval option to status line for periodic updates during idle periods

Bug Description
Feature: Status line refreshInterval option

The status line is awesome but it only updates on events (assistant messages, mode changes, etc). That means you can't show anything time-based during idle periods, which is when you're actually looking at it.

Would love a simple config option:

{
"statusLine": {
"refreshInterval": 30
}
}

Just re-runs the script every N seconds even when idle. Default 0 to keep current behavior.

My use case: I want to track the 5-min prompt cache TTL so I can send my next message while the cache is still warm. Right now there's no way to surface that in the status line since it goes stale the moment Claude stops responding.

It's useful beyond caching too. Elapsed timers, system monitors, whatever. The whole script execution pipeline already exists, it just needs a setInterval on top of it.

Environment Info

• Platform: win32
• Terminal: vscode
• Version: 2.1.58
• Feedback ID: f6961575-e004-42e6-84b6-0ae89464b401