Add Tailwind v4 @theme tokens for surfaces, accents, text, borders,
and status colors. Self-host Geist Sans/Mono variable fonts. Redesign
nav with backdrop blur and active states, home page with gradient hero.
Migrate all 50+ components from ad-hoc gray/blue Tailwind classes to
semantic theme tokens (surface-*, text-*, border-*, accent-*, status-*).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
