fix(usage-status): prevent crash on Pi reload from stale ExtensionContext

[rnavarro]

Pi crashes on reload when the usage-status extension's setInterval timer fires with an ExtensionContext that has gone stale. The ExtensionContext.hasUI getter calls assertActive(), which throws after session replacement or reload.

I hit this when reloading Pi after switching providers with Ctrl+P. Pi would crash immediately with:

Error: This extension ctx is stale after session replacement or reload.
  at ExtensionRunner.assertActive (runner.js:297)

The timer callback and several other code paths accessed captured ctx properties (hasUI, ui.setStatus, modelRegistry) without checking liveness. A ctx that becomes stale during an async gap (e.g., after await getSyntheticApiKey) also caused unhandled rejections from the catch block re-touching ctx.ui.

Fix: Add isCtxLive() helper that safely probes hasUI in a try/catch to detect stale contexts, and apply it at every entry point that touches a captured ExtensionContext:

• setInterval callback: isCtxLive guard before updateFooterStatus
• stopAutoRefresh(): clear activeContext; guard ctx.ui access
• updateFooterStatus(): isCtxLive at entry and after each await
• updateFooterStatus() catch: guard against double-throw on stale ctx
• updateFooterStatus() queuedRefresh: use activeContext instead of the captured ctx parameter (which may belong to a prior session)
• setLoadingStatus(): isCtxLive after await
• renderFromLastSnapshot(): isCtxLive guard
• SYNTHETIC_CONFIG_UPDATED_EVENT handler: isCtxLive on currentContext

14 new tests cover the stale context guard, stop behavior, mid-session staleness, stopAutoRefresh with stale ctx, and non-UI mode (hasUI=false on a live context).

[aliou]

Hey @rnavarro, thank you for the PR! But instead of keeping using a potentially stale extension context, the data will no longer be polled, but live updated by calls to the provider. This is handled in #44 and #52 , that are going to be merged in the release tomorrow morning.

[rnavarro]

Nice! Good stuff, thanks for all you do on this extension!