fix(updater): anchor WinUI runtime so transient dialog close doesn't kill in-flight download (#644)

UpdateDialog is a WindowEx (its own full WinUI Window), not a ContentDialog.
On the startup update path it is the only window in the process. WinUI 3
Desktop's default DispatcherShutdownMode is OnLastWindowClose, so clicking
'Download' (which calls Close() on the dialog) shuts down the WinUI runtime
mid-extraction. The Updatum-managed ZipFile.ExtractToDirectory only got
~199 of 1505 files written to %TEMP% before the process was terminated,
the .bat script that drives the in-place file replacement was never
written, and the install dir was never updated. Because the shutdown
came from the native side it bypassed AppDomain.ProcessExit, so no
'Process exiting (ExitCode=...)' line was logged and no managed
exception was thrown, making the failure silent.

Switch the DispatcherShutdownMode to OnExplicitShutdown so the runtime
only exits when we call Application.Exit() (which we already do in the
existing shutdown paths). The keep-alive window remains because it is
still required as a persistent XamlRoot host for ContentDialogs that
fire when no Hub window is open.

Verified on Windows by upgrading v0.5.1 -> v0.6.0:
  (Get-Item ".\OpenClaw.Tray.WinUI.exe").VersionInfo.ProductVersion
  0.6.0+...

Co-authored-by: Keith Mahoney <you@example.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: 3 people

src/OpenClaw.Tray.WinUI/App.xaml.cs

@@ -374,6 +374,16 @@ _dispatcherQueue is null
         // Register URI scheme on first run
         DeepLinkHandler.RegisterUriScheme();
 
+        // Anchor the WinUI runtime so transient windows (UpdateDialog,
+        // setup wizard, etc.) don't terminate the process when closed.
+        // WinUI 3 Desktop's default DispatcherShutdownMode is
+        // OnLastWindowClose — without this override, closing the
+        // UpdateDialog on the startup path (when it is the only window)
+        // would shut down the WinUI runtime mid-flight and kill the
+        // in-progress download/extraction. We still control shutdown
+        // explicitly via Application.Exit().
+        DispatcherShutdownMode = DispatcherShutdownMode.OnExplicitShutdown;
+
         // Check for updates before launching. Skip in test instances — no UI dialogs,
         // no network calls, no startup delay.
         if (DataDirOverride is null &&