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

@@ -90,7 +90,7 @@ internal partial class ContentBrowserViewModel : ObservableObject
                         if (!isDir)
                         {
                             var ext = Path.GetExtension(fullPath);
-                            assetType = AssetHandlerRegistry.GetAssetTypeByExtension(ext);
+                            assetType = AssetHandlerRegistry.GetRuntimeAssetTypeByExtension(ext);
                         }
                         Files.Add(new ExplorerItem(Path.GetFileName(fullPath), fullPath, isDir, assetType));
                     }
@@ -144,7 +144,7 @@ internal partial class ContentBrowserViewModel : ObservableObject
             }
 
             var ext = Path.GetExtension(file);
-            var assetType = AssetHandlerRegistry.GetAssetTypeByExtension(ext);
+            var assetType = AssetHandlerRegistry.GetRuntimeAssetTypeByExtension(ext);
 
             var fileItem = new ExplorerItem(Path.GetFileName(file), file, false, assetType);
             Files.Add(fileItem);