docs: modernize landing page visuals and scroll experience

- Remove hero stats bar (carried over from chore/remove-aieb-benchmark)
- Inline design-token fallbacks so the page keeps its palette even if
  the shared tokens stylesheet fails to load
- Hero: layered radial glows, fluid clamp() type scale, animated
  gradient sheen on the title (reduced-motion aware), elevated
  install block with hover glow
- Sticky section nav: glassmorphism (backdrop-filter + @supports
  fallback), pill links, scrollspy active-section highlighting
- Cards/doc-links/table/cmd-list: hover lift, glow and row highlights
- Terminal carousels: deeper window shadow, gradient title bar,
  glowing active dot, thin scrollbars, aria-labelled dot buttons,
  auto-rotation disabled under prefers-reduced-motion
- Scroll experience: smooth scrolling + scroll-padding for anchor
  jumps, staggered IntersectionObserver reveal (JS-gated, no-JS
  fallback shows content), hover anchor links on section headings,
  back-to-top button
- Accessibility: :focus-visible outlines, selection color, full
  prefers-reduced-motion coverage for every added animation

Author: jkyberneees