pwsh.exe hardcoded in 6 places - CLI completely unusable on Windows 11 with only PowerShell 5.1 (closed #411 is still broken in v0.0.417)

### Describe the bug

Issue #411 was closed as "not_planned" in Oct 2025, but the bug is still present and getting worse — it now blocks the CLI from running **any shell command at all** on Windows machines that ship only with Windows PowerShell 5.1 (`powershell.exe`).

The error on every single command:

首先檢查 ~/.copilot/pkg/universal/{version}/index.js 中列出的六個 pwsh.exe 參照，並僅使用 Windows PowerShell 5.1 在 Windows 11 上重現失敗。將這些呼叫追溯回專案原始碼，而不是只編輯產生的 bundle。完成的標準是：shell 命令和版本檢查無需 pwsh.exe 即可正常運作，包括 detached 命令和 PTY 啟動。

由索引模型根據 Issue 內容生成。