feat: Feature 3.1 — Landing page + blog + Phase 3 specs

Next.js 14+ web app in web/ directory:
- Landing page: Hero, How It Works, Features, 3-tier Pricing with
  founder badges, Footer with email capture
- Blog system: MDX-powered, /blog index + /blog/[slug] pages,
  reading time, Open Graph tags, JSON-LD structured data
- Auth pages: /login + /signup (Supabase Auth ready)
- Design system: dark theme, grade colors (A/B/C/D), BetonBLK voice
- 1 seed blog post: "How to Read Line Movement Like a Sharp"
- Specs for 3.2 (Scan UI), 3.3 (Bet Tracker), 3.4 (Stripe)

Build passes clean: 7 static pages generated.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

web/postcss.config.mjs

@@ -0,0 +1,7 @@
+const config = {
+  plugins: {
+    "@tailwindcss/postcss": {},
+  },
+};
+
+export default config;