fix(ui): hide quick switch buttons for disconnected monitors

Filter quick switch items to only show buttons for monitors that are currently connected. This prevents users from attempting to switch inputs on monitors that are no longer available.

MonitorControl/MainWindow.xaml.cs

@@ -438,6 +438,10 @@ public partial class MainWindow : Window
         quickSwitchPanel.Children.Clear();
         var quickItems = MonitorConfigManager.GetQuickSwitchItems();
 
+        // Only show buttons for monitors that are currently connected
+        var connectedSerials = new HashSet<string>(_loadedMonitors.Select(m => m.Monitor.SerialNumber));
+        quickItems = quickItems.Where(i => connectedSerials.Contains(i.MonitorSerialNumber)).ToList();
+
         if (quickItems.Count == 0)
         {
             quickSwitchPanel.Visibility = Visibility.Collapsed;