A page's own reduced-motion reset never crosses a shadow boundary, so library components rendered inside
custom elements slid, faded and spun for readers who asked for less motion: thirteen of them, including the
legends and map controls (regions-plugin found it on ProgressBar and named the class).
useShadowStyles now injects one prefers-reduced-motion reset into each shadow root it styles, which covers
every component styled through it, including later ones. PosterDialog, FilterDropdown and SearchFilterHeader
style themselves with <style> blocks and carry their own guard.
check:shadow-reduced-motion (in gates:pre): useShadowStyles must inject the reset, and every animating
library component must be covered. It fails without the reset (negative-tested) and found the three
<style>-block components on its first run.
