Add CharacterVisualDescriptor (11-variant BodyType enum, wire format
encode/decode, body_type_key mapping) and CharacterVisual compositor
(runtime 3D character assembler with slot architecture, BoneAttachment3D,
clothing coverage, recolor mask loading, skin tone tinting, bone
validation). Includes 64 unit tests and Blender utility scripts.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
