fix(panel): mark panels dirty on window add/close

TaskBarElement was not updating when windows were created or closed
at runtime because WindowStateService never notified panels. Add
PanelStateService.MarkDirty() calls to AddWindow and CloseWindow.

Author: nickprotop

SharpConsoleUI/Core/WindowStateService.cs

@@ -931,6 +931,9 @@ 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;
 	}
@@ -1039,6 +1042,9 @@ 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)
 		{