Settings: group preferences and open from gear

Group App Settings by purpose and let right-click on the gear open settings directly while preserving the left-click menu.

WPF event reference: https://learn.microsoft.com/en-us/dotnet/api/system.windows.uielement.previewmouserightbuttondown?view=windowsdesktop-10.0

Controls/TopBar.xaml.cs

@@ -26,6 +26,14 @@ public partial class TopBar : UserControl
         _ = LoadAvatarImageAsync();
     }
 
+    private void GearButton_PreviewMouseRightButtonDown(object sender, System.Windows.Input.MouseButtonEventArgs e)
+    {
+        // Right-click goes straight to App Settings; the menu stays on left-click.
+        e.Handled = true;
+        if (DataContext is MainViewModel { OpenSettingsCommand: { } open } && open.CanExecute(null))
+            open.Execute(null);
+    }
+
     private void GearButton_Click(object sender, RoutedEventArgs e)
     {
         // One menu (Settings / Bug / Feature / About), opened on click — moved up