live-reload scroll restore hides play-once scroll reveals

When developing with a live-reload/auto-refresh preview, the browser restores scroll position on reload. So a play-once reveal (IntersectionObserver or a one-shot scroll check that adds a class when an element enters view) fires at load because the element is already in view after the scroll is restored. You then never see the entrance animation and think it is broken, when it actually works on a fresh top-of-page load. Two fixes: (1) scrub the effect to scroll progress (map opacity/translate to how far the element is into the viewport via getBoundingClientRect) so it is visible whenever you scroll through it, never a one-shot; (2) note IntersectionObserver often does not fire under headless Chrome --virtual-time-budget, so verify reveals with a scroll-position approach instead. Unrelated bug same session: scoped section CSS written as #name{...} silently does nothing if the element has a different id (e.g. id=install) even though its class matches; match the id or scope by class.