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/Runtime/Ghost.Engine/Components/GPUInstanceRef.cs

@@ -1,8 +1,11 @@
+using Ghost.Core;
 using Ghost.Entities;
+using Ghost.Graphics.Services;
 
 namespace Ghost.Engine.Components;
 
 public struct GPUInstanceRef : IComponent
 {
-    public uint gpuSceneIndex;
+    public uint gpuInstanceIndex;
+    public Identifier<MaterialPalette> materialPalette;
 }