Replace fox skinned sample with Cesium Man

[anirul]

Summary

• replace the fox skinned sample with a higher-detail Cesium Man asset
• fix skinned glTF import so helper transforms are not double-applied to skinned meshes
• correct the remaining skinning root handling for the CesiumMan hierarchy and update the sample tests/docs

Details

The sample now uses asset/model/cesium_man/CesiumMan.glb in asset/json/skinned_mesh.json and the related docs/tests have been updated to stop assuming the old fox mesh and clip naming.

On the loader side, skinned meshes now stay in bind/local space instead of baking imported mesh transforms into the source vertices. The remaining CesiumMan pose issue was then fixed by stopping the extra global-inverse correction from being injected into the skinning path for this imported glTF hierarchy.

Verification

• FrameOpenGLTest --gtest_filter="SkinnedMeshTest.*:OpenGLRayTracingLevelTest.SkinnedMesh*"
• FrameVulkanTest --gtest_filter="VulkanSkinnedRayTracingParseTest.*"
• 03_SkinnedMesh.exe --auto_exit_seconds=4 visual smoke check