Refactor mesh import, meshlet, and asset handler systems

- Mesh import now builds full node hierarchy and splits geometry by material, with robust normal/tangent handling
- Meshlet generation supports material indices for correct assignment
- Refactored texture cube map compression and mipmap handling
- Updated asset handler registration to new namespace
- Enabled asset reimport on import events
- Improved code quality, resource management, and formatting

src/Editor/Ghost.Editor/ActivationHandler.cs

@@ -66,13 +66,13 @@ internal static class ActivationHandler
 
         AllocationManager.Initialize(opts);
 
-        //var assetRegistry = App.GetService<IAssetRegistry>();
-        //var engineCore = App.GetService<EngineCore>();
+        var assetRegistry = App.GetService<IAssetRegistry>();
+        var engineCore = App.GetService<EngineCore>();
 
-        //assetRegistry.OnAssetImported += (sender, e) =>
-        //{
-        //    engineCore.AssetManager.ReimportAsset(e);
-        //};
+        assetRegistry.OnAssetImported += (sender, e) =>
+        {
+            engineCore.AssetManager.ReimportAsset(e);
+        };
 
         return ValueTask.CompletedTask;
     }

src/Editor/Ghost.Editor/ViewModels/Controls/ContentBrowserViewModel.cs

@@ -1,13 +1,13 @@
 using CommunityToolkit.Mvvm.ComponentModel;
+using Ghost.Core.Utilities;
 using Ghost.Editor.Core;
+using Ghost.Editor.Core.Assets;
 using Ghost.Editor.Core.Contracts;
 using Ghost.Editor.Core.Utilities;
 using Ghost.Editor.Models;
-using Ghost.Editor.Core.AssetHandler;
-using System.Collections.ObjectModel;
-using Microsoft.UI.Dispatching;
 using Ghost.Engine;
-using Ghost.Core.Utilities;
+using Microsoft.UI.Dispatching;
+using System.Collections.ObjectModel;
 
 namespace Ghost.Editor.ViewModels.Controls;
 
@@ -69,7 +69,7 @@ internal partial class ContentBrowserViewModel : ObservableObject
 
         var fullPath = PathUtility.Normalize(e.AssetPath);
         var dirPath = Path.GetDirectoryName(fullPath);
-        
+
         if (string.Equals(dirPath, CurrentDirectoryPath, StringComparison.OrdinalIgnoreCase))
         {
             _dispatcherQueue.TryEnqueue(() =>
@@ -86,7 +86,7 @@ internal partial class ContentBrowserViewModel : ObservableObject
                     if (!Files.Any(f => string.Equals(f.Path, fullPath, StringComparison.OrdinalIgnoreCase)))
                     {
                         var isDir = Directory.Exists(fullPath);
-                        AssetType assetType = AssetType.Unknown;
+                        var assetType = AssetType.Unknown;
                         if (!isDir)
                         {
                             var ext = Path.GetExtension(fullPath);