AltGr key combinations not working on Windows Terminal (de-AT locale)

### Describe the bug

AltGr key combinations do not produce any characters inside the Copilot CLI input when the CLI is launched from Powershell Core within Windows Terminal.
For example, AltGr+Q (which should produce @) and AltGr+M (which should produce µ) are silently swallowed -- nothing is inserted. This affects all AltGr combinations, not just specific keys. The same setup works correctly in IntelliJ's integrated PowerShell terminal on the same machine.

AltGr key combinations do work when typing in the Windows Terminal itself.

### Affected version

1.0.14

### Steps to reproduce the behavior

1. Use a German-Austrian (de-AT) keyboard layout on Windows
2. Open Windows Terminal (PowerShell profile)
3. Launch copilot
4. Try typing AltGr+Q to insert @
5. Nothing is inserted -- the keypress is silently consumed
6. Same happens with any other AltGr combination (e.g., AltGr+M for µ)

```
Add-Type -TypeDefinition 'using System; using System.Runtime.InteropServices; public class KbdHelper { [DllImport("user32.dll")] public static extern IntPtr GetKeyboardLayout(uint idThread); }'; '{0:X}' -f
[int64][KbdHelper]::GetKeyboardLayout(0)
```
returns `4070409` (both in Windows Terminal, IntelliJ's Terminal integration, and when asking Copilot to run it)

- High word 0407 → German (Austria) locale
- Low word 0409 → US English keyboard layout

So it seems that Copilot CLI here ignores to locale part.

### Expected behavior

_No response_

### Additional context

_No response_