feat: Racing Cards landing page - Astro + Tailwind v4

- Mobile-first dark mode landing
- Lucide icons (zero emojis)
- Self-hostable (Dockerfile + nginx)
- 10 card images generated with Nano Banana 2
- Sections: Hero, How It Works, Card Gallery, Features, Early Access, Footer
- Simple HTML form (no Netlify dependency)
- Zero JS output, static HTML

public/favicon.svg

@@ -0,0 +1,4 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 32 32">
+  <rect width="32" height="32" rx="6" fill="#0a0a12"/>
+  <text x="16" y="23" text-anchor="middle" font-size="20" font-family="sans-serif" font-weight="bold" fill="#e10600">R</text>
+</svg>