Extends the WMO normal mapping/POM system to character M2 models with
bone-skinned tangents. Auto-generates normal/height maps from diffuse
textures using luminance→height, Sobel→normals (same algorithm as WMO).
- Expand vertex buffer from M2Vertex (48B) to CharVertexGPU (56B) with
tangent vec4 computed via Lengyel's method in setupModelBuffers()
- Tangents are bone-transformed and Gram-Schmidt orthogonalized in the
vertex shader, output as TBN for fragment shader consumption
- Fragment shader gains POM ray marching, normal map blending, and LOD
crossfade via dFdx/dFdy (identical to WMO shader)
- Descriptor set 1 extended with binding 2 for normal/height sampler
- Settings (enable, strength, POM quality) wired from game_screen.cpp
to both WMO and character renderers via shared UI controls
