Shell escape: support PowerShell scripts (.ps1) on Windows

[stalep]

Summary

The shell escape feature (#566) uses cmd /c on Windows, which correctly handles .bat and .cmd files. However, PowerShell scripts (.ps1) do not work with cmd /c — they require powershell -File or pwsh -File.

Current behavior

[myshell]$ !deploy.ps1
'deploy.ps1' is not recognized as an internal or external command

Expected behavior

[myshell]$ !deploy.ps1
Deploying to production...
Done.

Proposed approach

In executeNativeCommand(), detect the file extension of the first token:

• .bat / .cmd / no extension / built-in commands -> cmd /c command (current behavior)
• .ps1 -> powershell -File script.ps1 args... or pwsh -File script.ps1 args...

Auto-detect whether pwsh (PowerShell Core, cross-platform) or powershell (Windows PowerShell) is available.

Alternative

Instead of auto-detecting, add a setting for the shell command:

SettingsBuilder.builder()
    .shellEscapeCommand("pwsh", "-Command")  // override default sh/cmd

This would also support using bash on Windows (via WSL or Git Bash).

Context

Follow-up to #566 (shell escape via ! prefix).