When files encoded in Windows 1252 are edited, Copilot changes the encoding to UTF-8.

### Describe the bug

Copilot doesn't respect the original file encoding; it makes edits and changes the file format to UTF-8. I haven't found a prompt to prevent this from happening.

What it does, after saving the wrong file, is try to revert the encoding using scripts.

### Affected version

GitHub Copilot CLI 1.0.56.

### Steps to reproduce the behavior

1) Create a Windows1252 file and save in repo;
2) Ask the copilot to make changes.

### Expected behavior

Copilot needs to respect file encoding

### Additional context

_No response_

使用 Windows 1252 檔案在 GitHub Copilot CLI 1.0.56 中重現此問題，然後追蹤 Copilot 修改該檔案時使用的編輯與儲存路徑。確認編輯會保留原始編碼，並根據回報的重現步驟驗證行為；issue 中沒有指定來源檔案或測試。

由索引模型根據 Issue 內容生成。