Refactor material palette system with GPU indirection

Major overhaul of material palette management:
- Added two-buffer indirection (PaletteOffsetBuffer, MaterialIndexBuffer) for GPU material lookup, with incremental upload and resizing.
- MaterialPaletteStore now tracks dirty ranges, supports deferred slot reclamation, and exposes CPU-side arrays for upload.
- ResourceManager manages persistent GPU buffers and uploads only dirty subranges per frame.
- Updated HLSL and C# structs to use palette indices.
- Refactored systems/components to use new palette index and release logic.
- Added RenderContext.UploadBufferRange for partial uploads.
Minor: Fixed StbIApi interop signatures, updated test namespaces, and performed code cleanups.

src/Test/Ghost.UnitTest/AssetSystem/AssertRegistryTest.cs

@@ -1,4 +1,4 @@
-using Ghost.Editor.Core.AssetHandler;
+using Ghost.Editor.Core.Assets;
 using Ghost.Editor.Core.Contracts;
 using Ghost.Editor.Core.Services;
 

src/Test/Ghost.UnitTest/AssetSystem/AssetCatalogTests.cs

@@ -1,4 +1,4 @@
-using Ghost.Editor.Core.AssetHandler;
+using Ghost.Editor.Core.Assets;
 using Ghost.Editor.Core.Services;
 using Microsoft.Data.Sqlite;
 

src/Test/Ghost.UnitTest/AssetSystem/AssetMetaTests.cs

@@ -1,5 +1,4 @@
-using Ghost.Editor.Core.AssetHandler;
-using Microsoft.VisualStudio.TestTools.UnitTesting;
+using Ghost.Editor.Core.Assets;
 
 namespace Ghost.UnitTest.AssetSystem;
 

src/Test/Ghost.UnitTest/AssetSystem/ImportCoordinatorTests.cs

@@ -1,4 +1,4 @@
-using Ghost.Editor.Core.AssetHandler;
+using Ghost.Editor.Core.Assets;
 using Ghost.Editor.Core.Services;
 using Microsoft.Data.Sqlite;