Copying text clears the screen on certain codepages

### Describe the bug

When copying selected text on Windows, the screen appears to reset or clear unexpectedly. This happens on my machine with codepage 936 but not when it is 437

### Affected version

1.0.79-5

### Steps to reproduce the behavior

1. Change the default code page on Windows: Region -> Administrative -> Change system locale -> Chinese (Simplified, Mainland China)
2. Launch Copilot CLI in a terminal
3. Select and copy something

### Expected behavior

The screen shouldn't be cleared

### Additional context

_No response_

No source file or test is named. First reproduce the copy operation under Windows codepage 936 and compare it with codepage 437, then locate the CLI's terminal selection and copy handling. Done means copying selected text no longer clears or resets the screen under the reported locale.

Written by the indexing model from the issue text.