IME composition causes window flickering/shaking on Windows

## Description

When typing CJK characters (Chinese/Japanese/Korean) using Windows IME in the Copilot CLI, the terminal window visibly flickers/shakes on each keystroke during IME composition.

## Steps to Reproduce

1. Open Copilot CLI in Windows Terminal
2. Switch to a CJK input method (e.g., Microsoft Bopomofo / Pinyin)
3. Start typing Chinese characters
4. Observe the terminal window shaking/flickering as the IME candidate window appears

## Expected Behavior

The TUI should not re-render/redraw the entire frame during IME composition events. The input area should remain stable while the user is composing characters.

## Actual Behavior

Every IME composition event triggers a full TUI re-render, causing visible window flickering that makes the CLI uncomfortable to use with CJK input methods.

## Environment

- OS: Windows 11
- Terminal: Windows Terminal
- PowerShell: 7.6.1
- Copilot CLI: 1.0.40-0
- IME: Microsoft Bopomofo (Traditional Chinese)
- Code Page: 65001 (UTF-8)

## Impact

This significantly degrades UX for CJK users and discourages use of the CLI in non-English languages.

Comece reproduzindo o problema no Copilot CLI no Windows Terminal com a entrada Microsoft Bopomofo ou Pinyin. Rastreie como os eventos de composição do IME chegam ao caminho de redesenho da TUI e verifique se a composição não aciona mais uma nova renderização do frame inteiro. O trabalho estará concluído quando a composição CJK permanecer visualmente estável e a entrada comum continuar funcionando.

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