BatchConvert: persist settings when window is closed via X/Escape

The target format and function options were only saved by the Done and
Convert buttons. Closing the window any other way lost them - especially
in /batchconvertui mode, where the batch window is the main window and
nothing else flushes settings to disk on exit (in the embedded flow the
main window's close handler masked this).

Fixes #11699

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: niksedk

src/ui/Features/Tools/BatchConvert/BatchConvertViewModel.cs

@@ -2504,6 +2504,11 @@ internal void Onloaded(object? sender, RoutedEventArgs e)
     internal void OnClosing(object? sender, WindowClosingEventArgs e)
     {
         UiUtil.SaveWindowPosition(Window);
+
+        // Persist target format and function options also when the window is closed via
+        // X/Escape - especially important in /batchconvertui mode, where this window is the
+        // main window and nothing else flushes settings to disk on exit (#11699).
+        SaveSettings();
     }
 
     internal void ComboBoxSubtitleFormatChanged()