Design tokens + agent iteration hardening

- tokens.css: full token layer (type scale rem-based, palette, spacing, radii)
- App.css rebuilt token-driven; zero hardcoded colors/px font sizes
- readability preset: --root-font-size 112%; button matrix scrolls when narrow
- App.tsx split into real components (Hero, CodeSample, RightRail + reflow)
- light theme via [data-theme=light] overrides; topbar sun/moon toggle persisted
- scripts/check-tokens.mjs + npm run check (lint, token guard, tsc, build)
- AGENTS.md: token contract, check gate, preview workflow

package.json

@@ -7,6 +7,7 @@
     "dev": "vite",
     "build": "tsc -b && vite build",
     "lint": "oxlint",
+    "check": "oxlint && node scripts/check-tokens.mjs && npm run build",
     "preview": "vite preview"
   },
   "dependencies": {