Ports an Unreal Engine avatar project's Macro/Micro/Nano additive gaze
design to ARKit blend shapes: pure, seedable state machine in
src/lib/humanoid/eye/, a client wrapper owning the frame loop in
src/lib/client/humanoid/eye/, and a Three.js demo/debug playground at
/demo/humanoid (split into AvatarStateDemo + EyeSystemDemo so future
animation libraries get their own sibling demo). Updates HUMANOID.md
and ARCHITECTURE.md to describe animation libraries as sub-packages
nested under humanoid/<name> rather than separate top-level packages.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>