Show context/token usage indicator in VSCode extension's input bar

Quick thought on the VSCode extension. The CLI version shows context usage at the bottom of the screen as you go, something like "Context: 45% / 200k tokens used". The VSCode extension seems to track the same info internally (I can see it in the extension log as autocompact: tokens=...) but doesn't display it anywhere I can find.

Would be useful to put this in or near the input bar at the bottom of the panel, similar to where the CLI shows it. A few reasons it'd be handy:

• Matches what the CLI already does, so the two would feel more consistent
• Long sessions occasionally hit autocompact when you're not expecting it; knowing how full your context is gives you a chance to wrap up before it summarizes things away
• For folks tracking usage, having it visible is just nice

Looks like the data's already there, so this should mostly be a UI change rather than a measurement one.

Extension version 2.1.138.