修复: 同事机器无 pwsh 启动失败 0x80070002

- 探测优先 pwsh (PS7)，找不到回退 powershell (PS5，Windows 自带)
- 脚本仅用兼容语法 (Write-Host/cd)，PS5 可直接运行

internal/launch.go

@@ -105,6 +105,15 @@ func (a SessionAction) bashScript() string {
 
 // --- 启动辅助 ---
 
+// powershellExe 返回可用的 PowerShell 可执行文件名：优先 pwsh (PS7)，找不到则回退 powershell (PS5，Windows 自带)。
+// 脚本只用 $Host.UI.RawUI、Write-Host、cd 等兼容语法，PS5 也能跑。
+func powershellExe() string {
+	if _, err := exec.LookPath("pwsh"); err == nil {
+		return "pwsh"
+	}
+	return "powershell"
+}
+
 func launchInWtWithTitle(dir, tabTitle, script string) {
 	encoded := encodePSCommand(script)
 	color := fmt.Sprintf("#%02X%02X%02X", randRange(80, 255), randRange(80, 255), randRange(80, 255))
@@ -112,7 +121,7 @@ func launchInWtWithTitle(dir, tabTitle, script string) {
 	if tabTitle != "" {
 		args = append(args, "--title", tabTitle)
 	}
-	args = append(args, "pwsh", "-NoExit", "-EncodedCommand", encoded)
+	args = append(args, powershellExe(), "-NoExit", "-EncodedCommand", encoded)
 	cmd := exec.Command("wt.exe", args...)
 	if err := cmd.Start(); err != nil {
 		log.Printf("[u-tabs] launch fail: %v", err)