v0.1.8

Add the animated Collapsible component - a folding panel that eases open AND closed via an exact measured max-height (grid 0fr/1fr snaps shut on collapse in some browsers), with chevron rotation, ResizeObserver-tracked height, controlled/uncontrolled modes, and a reduced-motion guard. Exported from the package, bundled into styles.css, and documented in the docs + playground.