feat(asset): asset manager + registration generator

Add runtime AssetManager and AssetHandlerRegistrationGenerator source generator.
Update editor asset handler types and services to work with new registration
mechanism and asset catalog. Remove legacy contracts ICloneable and IReleasable.

Files added:
- src/Runtime/Ghost.Engine/AssetManager.cs
- src/Runtime/Ghost.Generator/AssetHandlerRegistrationGenerator.cs

Major edits:
- Editor asset handler classes and services (Asset*, Texture*, Registry)
- Runtime Handle.cs and project files
- Render graph executor and tests updated accordingly

This commit introduces the foundation for the modern asset pipeline
including generated registration of asset handlers and a centralized
runtime AssetManager that will drive asset lifecycle.

src/Editor/Ghost.Editor/App.xaml.cs

@@ -72,6 +72,7 @@ public partial class App : Application
 
                 services.AddTransient<ProjectBrowserViewModel>();
 
+                // TODO: Use source generators to generate this code at compile time instead of using reflection at runtime.
                 foreach (var type in TypeCache.GetTypes())
                 {
                     var data = type.GetCustomAttributesData().FirstOrDefault(a => a.AttributeType == typeof(EditorInjectionAttribute));

src/Editor/Ghost.Editor/Ghost.Editor.csproj

@@ -39,7 +39,7 @@
     <PackageReference Include="CommunityToolkit.WinUI.Controls.Primitives" Version="8.2.251219" />
     <PackageReference Include="CommunityToolkit.WinUI.Controls.Sizers" Version="8.2.251219" />
     <PackageReference Include="CommunityToolkit.WinUI.Controls.TabbedCommandBar" Version="8.2.251219" />
-    <PackageReference Include="Microsoft.Extensions.Hosting" Version="10.0.5" />
+    <PackageReference Include="Microsoft.Extensions.Hosting" Version="10.0.6" />
     <PackageReference Include="Microsoft.Windows.CsWinRT" Version="2.2.0" />
     <PackageReference Include="Microsoft.Windows.SDK.BuildTools" Version="10.0.28000.1721" />
     <PackageReference Include="Microsoft.WindowsAppSDK" Version="1.8.260317003" />