Use motion/react for JS Animations

Note the conditional in the rule: it does not say to reach for a JS animation library, it says which one to use once you have established that JS is required at all. CSS first; JS only when the interaction genuinely needs it (see animations-implementation-preference). When it does, hand-rolling with requestAnimationFrame or direct DOM writes means re-solving interruption, velocity hand-off, spring physics and gesture integration yourself — motion/react handles those, and the alternative is a pile of animations that restart from zero every time the user touches them.