docs-site: landing round 3 — brand chips, splash hamburger, cinematic scroll

- provider chips carry official simple-icons marks (Anthropic, Google, Kimi,
  Ollama, OpenRouter, DeepSeek); brands absent from the library stay text-only
- floating pill header gains a splash-only hamburger below the nav breakpoint,
  opening a near-opaque glass panel with every docs section (aria-expanded,
  Escape/outside close); docs pages keep the native Starlight toggle
- cinematic landing motion: hero copy recedes on scroll (scroll(root) timeline),
  hero photo settles from a slow zoom, terminal clip-path wipe, per-chip
  stagger, deeper slide reveals — all prefers-reduced-motion gated
- fix: lightningcss merged animation-timeline into the animation shorthand and
  killed scroll-driven motion; build now minifies CSS with esbuild
- fix: slide transforms widened the page at ~773px; .lp clips overflow-x
- hero copy centered with light 440 headline; panels/buttons near-opaque;
  demo capture crops to bottom focus