feat(ui): migrate ProjectBrowser to GridView, improve cleanup

Refactored ProjectBrowser to use GridView instead of ItemsView for file display, updated selection logic, and set a minimum grid height. FloatingWindow now manages DockingLayout cleanup on close to prevent resource leaks. Simplified DockDocument and DockGroup instantiations in EngineEditorWindow. Updated GetDirectoryNameConverter to use Path.GetDirectoryName directly. App shutdown now calls EditorApplication.Shutdown(). Added Ghost.Engine reference in ActivationHandler.

src/Editor/Ghost.Editor/ActivationHandler.cs

@@ -1,5 +1,6 @@
 using Ghost.Editor.Core.Utilities;
 using Ghost.Editor.Models;
+using Ghost.Engine;
 using Misaki.HighPerformance.LowLevel.Buffer;
 using System.Reflection;
 
@@ -62,11 +63,8 @@ internal static class ActivationHandler
 
         AllocationManager.Initialize(opts);
         TypeCache.Initialize();
-
-        // await ((Core.AssetHandle.AssetService)App.GetService<IAssetService>()).Init();
-
-        // TODO: Init other subsystems here.
-        // await Task.Delay(10000); // Wait 10 seconds to simulate work.
+        
+        //App.GetService<EngineCore>();
 
         return ValueTask.CompletedTask;
     }