feat(landing): full visual overhaul — Stripe/Linear polish pass

feat(landing): full visual overhaul — Stripe/Linear polish pass

Rewrites landing-pro.tsx with all 11 improvements approved in plan:
- Hero shows a real PR review card mock with syntax-highlighted diff,
  inline Claude comment, gate pills, and auto-merge banner
- Dark navy (#0a0d1a) closing CTA section breaks the all-white monotony
- Stroke-only SVG icons for all 8 platform groups
- Scroll-reveal (IntersectionObserver) on every card and section
- Counter animation (cubic ease-out, requestAnimationFrame) on hero stats
- Color-coded live-now cards (violet/green/brand/neutral left borders)
- Card hover lift (translateY -3px + deeper shadow) across all cards
- Richer AI feature mocks: avatar, file path, comment bubble, verdict badge
- Impact stat band: 2× faster · 100% audit · <30s AI review
- Pain table problem column in muted red, fix column in ink
- Typography: Inter Tight 800 H1, tighter letter-spacing throughout

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>