feat: redesign the site with an editorial, refined visual language (#50)

- typography: Fraunces variable serif for display (with italic gradient
  accents), properly self-hosted Inter for body, JetBrains Mono for
  code — all via next/font (previously Inter was declared but never
  loaded)
- atmosphere: layered radial glows, a faint champagne sheen, and fine
  SVG grain behind all content
- surfaces: gradient hairline borders, glass panels with backdrop blur,
  deeper layered shadows; refined terminal card with a slow idle drift
  (disabled under prefers-reduced-motion)
- details: pill buttons with inner light, sticky blurred nav, serif
  step numerals, dotted confidence pills, styled selection and
  scrollbar
- verified no horizontal overflow at 390px in a real browser; refresh
  the README desktop screenshot to match

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

Author: aryamthecodebreaker