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.Graphics/Shaders/Includes/Properties.hlsl

@@ -29,6 +29,8 @@ struct FrameData
 {
     BYTE_ADDRESS_BUFFER instanceBuffer;
     BYTE_ADDRESS_BUFFER userBuffer;
+    BYTE_ADDRESS_BUFFER paletteOffsetBuffer;   // global PaletteOffsetBuffer
+    BYTE_ADDRESS_BUFFER materialIndexBuffer;   // global MaterialIndexBuffer
 };
 
 struct ViewData
@@ -46,7 +48,7 @@ struct InstanceData
 {
     float4x4 localToWorld;
     BYTE_ADDRESS_BUFFER meshBuffer;
-    BYTE_ADDRESS_BUFFER materialBuffer;
+    uint materialPaletteIndex;  // index into PaletteOffsetBuffer
 };
 
 struct MeshData
@@ -59,6 +61,7 @@ struct MeshData
     BYTE_ADDRESS_BUFFER meshletBuffer;
     BYTE_ADDRESS_BUFFER meshletVerticesBuffer;
     BYTE_ADDRESS_BUFFER meshletTrianglesBuffer;
+    uint materialSlotCount;
 };
 
 #if defined(__GRAPHICS__)