refactor(panel): TaskBarElement subscribes to window events

Replace push-based MarkDirty() calls in WindowStateService with
event-driven approach. TaskBarElement now subscribes to WindowCreated,
WindowClosed, WindowActivated, and WindowStateChanged events from
WindowStateService, calling Invalidate() on change.

Author: nickprotop

SharpConsoleUI/Core/WindowStateService.cs

@@ -931,9 +931,6 @@ public Window AddWindow(Window window, bool activateWindow = true)
 
 		window.WindowIsAdded();
 
-		// Notify panels that window list changed (updates taskbar, etc.)
-		context.PanelStateService.MarkDirty();
-
 		_logService?.LogDebug($"Window added successfully: {window.Title}", "Window");
 		return window;
 	}
@@ -1042,9 +1039,6 @@ public bool CloseWindow(Window? window, bool activateParent = true, bool force =
 		// STEP 3: Complete the close (fire OnClosed, dispose controls)
 		window.CompleteClose();
 
-		// Notify panels that window list changed (updates taskbar, etc.)
-		context.PanelStateService.MarkDirty();
-
 		// Clear only the closed window's area (not entire screen!)
 		if (_renderer != null && _consoleDriver != null)
 		{

SharpConsoleUI/Panel/Elements/TaskBarElement.cs

@@ -1,3 +1,4 @@
+using SharpConsoleUI.Core;
 using SharpConsoleUI.Helpers;
 using SharpConsoleUI.Layout;
 using SharpConsoleUI.Parsing;
@@ -6,13 +7,15 @@ namespace SharpConsoleUI.Panel;
 
 /// <summary>
 /// A panel element that displays a clickable list of windows (task bar).
+/// Subscribes to WindowStateService events for automatic updates.
 /// </summary>
 public class TaskBarElement : PanelElement
 {
     private const int MaxTitleLength = 15;
     private const int TitleEllipsisLength = 7;
     private List<(Window window, int startX, int endX)> _windowPositions = new();
     private int _lastStateHash;
+    private WindowStateService? _subscribedService;
 
     /// <summary>
     /// Initializes a new TaskBarElement.
@@ -47,6 +50,8 @@ public override void Render(CharacterBuffer buffer, int x, int y, int width, Col
         if (WindowSystem == null || width <= 0)
             return;
 
+        EnsureSubscribed();
+
         _windowPositions.Clear();
 
         // Get top-level taskbar windows sorted by creation order
@@ -144,6 +149,36 @@ public override bool ProcessMouseEvent(Events.MouseEventArgs args, int elementX,
         return false;
     }
 
+    private void EnsureSubscribed()
+    {
+        var service = WindowSystem?.WindowStateService;
+        if (service == null || service == _subscribedService)
+            return;
+
+        Unsubscribe();
+        _subscribedService = service;
+        service.WindowCreated += OnWindowChanged;
+        service.WindowClosed += OnWindowChanged;
+        service.WindowActivated += OnWindowActivated;
+        service.WindowStateChanged += OnWindowStateChanged;
+    }
+
+    private void Unsubscribe()
+    {
+        if (_subscribedService != null)
+        {
+            _subscribedService.WindowCreated -= OnWindowChanged;
+            _subscribedService.WindowClosed -= OnWindowChanged;
+            _subscribedService.WindowActivated -= OnWindowActivated;
+            _subscribedService.WindowStateChanged -= OnWindowStateChanged;
+            _subscribedService = null;
+        }
+    }
+
+    private void OnWindowChanged(object? sender, WindowEventArgs e) => Invalidate();
+    private void OnWindowActivated(object? sender, WindowActivatedEventArgs e) => Invalidate();
+    private void OnWindowStateChanged(object? sender, WindowStateEventArgs e) => Invalidate();
+
     private static int ComputeStateHash(List<Window> windows)
     {
         unchecked