Add, fix, refactor, debug, test, or explain Flutter animations and motion effects. Use when working with implicit animations such as AnimatedContainer, AnimatedOpacity, AnimatedSwitcher, and TweenAnimationBuilder; explicit animations using AnimationController, Tween, CurvedAnimation, AnimatedWidget, AnimatedBuilder, and built-in transitions; Hero/shared-element route transitions; staggered or sequenced animations; physics-based motion, gestures, springs, flings, scroll physics, curves, performance, accessibility, reduced motion, and animation lifecycle bugs.