Read the ambient color from the MOHD chunk (BGRA uint32) and store it
on WMOModel as a normalized RGB vec3. Pass it through ModelData into
the per-batch WMOMaterialUBO (replacing the unused pad[3] bytes, keeping
the struct at 64 bytes). The GLSL interior branch now floors vertex
colors against the WMO ambient instead of a hardcoded 0.5, so dungeon
interiors respect the artist-specified ambient tint from the WMO root
rather than always clamping to grey.