Replace Magick.NET with stb_image; refactor asset pipeline

- Switched image loading/saving from Magick.NET to native stb_image (Ghost.StbI), removing Magick.NET dependency.
- Added Ghost.StbI project with native DLL, P/Invoke bindings, and wrapper.
- Refactored TextureAssetHandler and TextureProcessor for stb_image, memory-mapped IO, and HDR/16-bit support.
- Split IAssetHandler into IImportableAssetHandler and IPackableAssetHandler; updated interfaces to use FileStream.
- Added shader and mesh asset handlers (GraphicsShaderAssetHandler, ComputeShaderAssetHandler, FBXAssetHandler).
- Improved asset registry/catalog path handling and naming consistency.
- Updated asset import pipeline to use new interfaces and trigger engine reimport.
- Enhanced UI toolbar button styles and EditPage layout.
- Added StbIBindingTest, DisableRuntimeMarshalling, and native wrapper attributes.
- Updated wrapper generator for regex derivesFrom; added stbi.json config.
- Removed Magick.NET reference; added Ghost.StbI and Ghost.Ufbx references.
- Miscellaneous bugfixes and code cleanup.

src/Runtime/Ghost.Engine/AssetManager.cs

@@ -197,7 +197,7 @@ internal unsafe partial class AssetEntry
 
         if (Interlocked.CompareExchange(ref _pendingReimport, false, true))
         {
-            _assetManager.InvalidateAsset(_assetId);  // re-queue
+            _assetManager.ReimportAsset(_assetId);  // re-queue
         }
     }
 
@@ -415,7 +415,7 @@ internal partial class AssetManager : IDisposable
         return entry;
     }
 
-    public void InvalidateAsset(Guid guid)
+    public void ReimportAsset(Guid guid)
     {
         if (!_entries.TryGetValue(guid, out var entry))
         {

src/Runtime/Ghost.Engine/EngineCore.cs

@@ -4,6 +4,12 @@ using Misaki.HighPerformance.Jobs;
 
 namespace Ghost.Engine;
 
+public interface IRuntimeInitializeCallback
+{
+    void Initialize();
+    void Shutdown();
+}
+
 public sealed partial class EngineCore : IDisposable
 {
     private readonly IContentProvider _contentProvider;
@@ -13,6 +19,10 @@ public sealed partial class EngineCore : IDisposable
     private readonly RenderSystem _renderSystem;
     private readonly AssetManager _assetManager;
 
+    internal JobScheduler JobScheduler => _jobScheduler;
+    internal RenderSystem RenderSystem => _renderSystem;
+    internal AssetManager AssetManager => _assetManager;
+
     public EngineCore(IContentProvider contentProvider)
     {
         _contentProvider = contentProvider;

src/Runtime/Ghost.Engine/TestSetup.cs

@@ -0,0 +1,13 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace Ghost.Engine;
+
+internal class TestSetup : IDisposable
+{
+    public void Dispose()
+    {
+        throw new NotImplementedException();
+    }
+}