fix(desktop): silence wsl.exe stderr banner + detached explorer relaunch rung

Follow-ups to the salvaged WSL-bridge gating (#66447):
- wsl-path-bridge.ts: discard wsl.exe stderr so the 'WSL is not installed'
  banner can never leak into an attached console on WSL-less machines (#80184).
- scripts/desktop-update/windows.ps1: add an explorer.exe-mediated detached
  relaunch rung between the WMI attempt and the tethered Start-Process
  fallback. When Win32_Process.Create fails (observed ReturnValue 8), the
  Desktop no longer re-attaches to the hand-off console, so its stdout stops
  flooding the window and the console can close.

scripts/desktop-update/windows.ps1

@@ -571,6 +571,59 @@ function Start-DesktopRelaunch {
     } catch {
         Write-HandoffLog "WARNING: WMI relaunch failed: $($_.Exception.Message); falling back"
     }
+    if (-not $spawned) {
+        # Middle rung: explorer.exe-mediated launch. On some machines
+        # Win32_Process.Create fails outright (observed ReturnValue 8,
+        # "unknown failure"), and the tethered fallback below re-attaches the
+        # Desktop to this console — its stdout then floods the console and the
+        # window can't close while the app lives. Explorer re-parents the
+        # target exactly like a normal shell launch, giving the same
+        # no-console detachment WMI would have. Explorer returns no pid, so
+        # verify by watching for a fresh Hermes process.
+        try {
+            $exeName = [System.IO.Path]::GetFileNameWithoutExtension($RelaunchExe)
+            $before = @(Get-Process -Name $exeName -ErrorAction SilentlyContinue | ForEach-Object { $_.Id })
+            Start-Process -FilePath 'explorer.exe' -ArgumentList ('"{0}"' -f $RelaunchExe) | Out-Null
+            $explorerDeadline = (Get-Date).AddSeconds(15)
+            while ((Get-Date) -lt $explorerDeadline) {
+                $fresh = @(Get-Process -Name $exeName -ErrorAction SilentlyContinue | Where-Object { $before -notcontains $_.Id })
+                if ($fresh.Count -gt 0) {
+                    Write-HandoffLog "desktop relaunched detached via explorer (pid $($fresh[0].Id))"
+                    $spawned = $true
+                    # Same foreground hand-off as the WMI rung: the new process
+                    # starts unfocused and only the current foreground owner
+                    # (us) can delegate that right.
+                    try {
+                        if ($script:Win32) {
+                            [HermesHandoff.Win32]::AllowSetForegroundWindow([int]$fresh[0].Id) | Out-Null
+                            $focusDeadline = (Get-Date).AddSeconds(20)
+                            while ((Get-Date) -lt $focusDeadline) {
+                                $hwnd = [System.IntPtr]::Zero
+                                try { $hwnd = (Get-Process -Id $fresh[0].Id -ErrorAction Stop).MainWindowHandle } catch { break }
+                                if ($hwnd -ne [System.IntPtr]::Zero) {
+                                    [HermesHandoff.Win32]::ShowWindow($hwnd, 9) | Out-Null  # SW_RESTORE
+                                    [HermesHandoff.Win32]::SetForegroundWindow($hwnd) | Out-Null
+                                    Write-HandoffLog "focused relaunched desktop window"
+                                    break
+                                }
+                                Start-Sleep -Milliseconds 400
+                            }
+                        }
+                    } catch {
+                        Write-HandoffLog "WARNING: could not focus relaunched desktop: $($_.Exception.Message)"
+                    }
+                    break
+                }
+                Start-Sleep -Milliseconds 400
+                if ($script:Ui) { [System.Windows.Forms.Application]::DoEvents() }
+            }
+            if (-not $spawned) {
+                Write-HandoffLog "WARNING: explorer relaunch did not produce a $exeName process; falling back"
+            }
+        } catch {
+            Write-HandoffLog "WARNING: explorer relaunch failed: $($_.Exception.Message); falling back"
+        }
+    }
     if (-not $spawned) {
         try {
             # Fallback keeps the old behavior (console tie-in and all) --