Fix: volume slider click-to-position restored

Skip Thumb clicks (let drag work normally), set value + e.Handled on
track clicks so the RepeatButton's IncreaseLarge/DecreaseLarge can't
override the jumped-to position.

207 tests, 0 warnings.

MainWindow.xaml.cs

@@ -123,11 +123,14 @@ public partial class MainWindow : Window
 
     private static void SetSliderValueFromClick(Slider slider, MouseButtonEventArgs e)
     {
+        if (e.OriginalSource is System.Windows.Controls.Primitives.Thumb)
+            return;
         var track = slider.Template.FindName("PART_Track", slider) as System.Windows.Controls.Primitives.Track;
         if (track == null) return;
         var pos = e.GetPosition(track);
         var fraction = Math.Clamp(pos.X / track.RenderSize.Width, 0, 1);
         slider.Value = slider.Minimum + fraction * (slider.Maximum - slider.Minimum);
+        e.Handled = true;
     }
 
     private void MicSpeaker_MouseLeftButtonUp(object sender, MouseButtonEventArgs e)