Agent Skills: threejs-animation

three.js keyframe animation system: AnimationMixer, AnimationClip, AnimationAction, KeyframeTrack variants, PropertyBinding, PropertyMixer, AnimationObjectGroup, AnimationUtils; mixing and crossfading clips, loop modes, timeScale, weight; addon AnimationClipCreator and CCDIKSolver for procedural rigs. Use when playing glTF clips, blending actions, or authoring procedural tracks; for skin deformation rigging on meshes see threejs-objects; for math interpolants without clips see threejs-math only when not tied to AnimationMixer.