Long text is not scrolling inside the input

### Describe the bug

When the textarea contains enough content to overflow, scrolling with the mouse wheel/trackpad does not scroll inside the textarea. Instead, the outer chat view/page scrolls, which makes editing longer prompts difficult.

### Affected version

1.0.63

### Steps to reproduce the behavior

1. Open GitHub Copilot CLI chat.
2. Type or paste enough text into the textarea so that the input area becomes scrollable.
3. Move the cursor over the textarea.
4. Try to scroll with the mouse wheel or trackpad.

### Expected behavior

The textarea should capture the scroll event and scroll its own content while the pointer is focused/hovering over it.

### Additional context

OS: MacOS 15.7.7
Terminal emulator: Terminal
Shell: zsh

在 GitHub Copilot CLI chat 中使用包含長值的 textarea 重現此問題，然後找出 chat 輸入框及其捲動或 wheel-event 處理邏輯。在回報的 macOS Terminal 和 zsh 設定上驗證此行為；完成的標準是，在內容溢出的 textarea 上進行滑鼠滾輪或觸控板操作時，捲動的是該 textarea，而不是外層 chat 檢視。

由索引模型根據 Issue 內容生成。