The hero, details bento and roadmap become scenes on a sticky stage that
crossfade as you scroll, while the light rays, orbit and tiles stay put.
An IntersectionObserver on one marker per scene picks the current scene;
nothing runs per scroll frame. Keyboard focus scrolls to the scene that
holds it, and the rays pause once the hero is behind.

Screens under 1280x800 and reduced motion keep the stacked page.
LibraryExplorer and HeroStage become HomeHero and HomeStory, and
LightRays gains a paused prop.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>