Wraps header and hero in a .hero-shell grid so the nav overlays the
mast gradient when integrated. On scroll, adds site-header--scrolled
which snaps to position: fixed; @keyframes drive the glass fade-in and
translateY slide since CSS transitions don't survive a simultaneous
position reflow. Exit is instant (user is near scroll-top, sticky
re-appears at the same visual position). Includes rAF-coalesced scroll
handler and full prefers-reduced-motion support.

Add hero whisper and footer tagline; warm FAQ eyebrow; devtools console nod.
Smooth staggered reveals and scroll entrances; hover feedback on highlights,
logo, demo iframe, and buttons; respect prefers-reduced-motion.