Accessibility: Screen reader reads premium requests status bar on every keypress instead of typed character

## Summary

When typing in the Copilot CLI input prompt, the screen reader announces the **premium requests status bar value** (e.g. `36.03333333333333 %`) on every single keypress, instead of echoing the character that was typed. This makes the CLI unusable for blind users.

## Root cause

The premium requests / quota status bar at the bottom of the UI is being re-rendered on every keypress. Screen readers (VoiceOver, NVDA, etc.) intercept that terminal output update and read it aloud, suppressing the expected character echo.

## Expected behavior

Typing `a` → screen reader says "a". The status bar should be invisible to the accessibility tree / screen reader during active text input.

## Actual behavior

Typing any character → screen reader announces the premium requests percentage (e.g. `36.03333333333333 %`) every single time. The user receives no feedback about what they are actually typing.

## Impact

**Critical accessibility regression for blind users.** The CLI is completely unusable with a screen reader because there is no way to know what you are typing.

## Steps to reproduce

1. Enable VoiceOver (macOS) or NVDA (Windows)
2. Launch Copilot CLI
3. Type any character in the input prompt
4. Screen reader announces the premium requests percentage instead of the typed character

## Suggested fix

- Mark the status bar region as `aria-hidden` or equivalent for terminal accessibility
- Only update the status bar when the user is **not** actively typing, or throttle updates
- Ensure the terminal input line has proper focus so character echo reaches the screen reader first
- Do not re-render the status bar on every single keystroke

## Reported by

A blind user relying on VoiceOver for all terminal interaction.