Powershell scripts fail with "AuthorizationManager check failed" on Windows using MXC sandbox

I've set up Copilot CLI to use the new MXC sandbox on Windows insiders.

## Issue
When the agent is trying to run a powershell script like `.\MyScript.ps1` it gets a sandbox error in return.
```powershell
AuthorizationManager check failed.
CategoryInfo: SecurityError
FullyQualifiedErrorId: UnauthorizedAccess
Exit code: 1
```

## Workaround
After some digging it seems to be causes by powershell not being able to read the registry, so it can't get the current execution profile.
I changed `.copilot\settings.json` to set the ExecutionPolicy at launch and that worked.
```json
{
...
"powershellFlags": [
"-NoProfile",
"-NoLogo",
"-ExecutionPolicy",
"RemoteSigned"
],
...
}
```

Not sure what is a good fix here. Maybe copilot should load the execution policy from the user profile and inject it directly instead of letting powershell try to read it from registry?

在启用 MXC sandbox 的 Windows Insiders 上运行 .\\MyScript.ps1 脚本以重现该故障。从 .copilot/settings.json 和 powershellFlags 配置开始，将失败的启动与使用 -NoProfile 和 -ExecutionPolicy RemoteSigned 的变通方法进行比较。完成标准是 PowerShell 脚本在 sandbox 保持启用的情况下运行时不再出现 AuthorizationManager 错误。

由索引模型根据 Issue 内容生成。