Selected text doesn't contrast well with the background

### Describe the bug

I'm running from Windows Terminal. Even setting the theme to high contrast, the difference between the background, the selected text background, and the text is not great:

Using the default theme, it's even worse:

### Affected version

Copilot CLI v1.0.22

### Steps to reproduce the behavior

1. copilot
2. select some text in the session

### Expected behavior

I'd like to have the same behavior as Windows Terminal:

### Additional context

This is Windows, running Terminal, in PowerShell 7.4.14. Color Scheme is Campbell

Start by reproducing the issue with the `copilot` command in Windows Terminal under PowerShell 7.4.14, then trace the session text-selection rendering. The work is done when selected text has contrast comparable to Windows Terminal in both the default and high-contrast themes, with coverage for the reported case if the project provides a relevant test entry point.

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