Rebuild website from scratch on Tailwind v4 + shadcn/ui

- Fresh Astro 5 project with Tailwind v4 and shadcn/ui olive preset
- All shadcn components installed (Card, Button, Badge, Separator, etc.)
- Homepage with hero, terminal demo, workflows, agents, sources, compute
- Full docs system with 24 markdown pages across 5 sections
- Sidebar navigation with active state highlighting
- Prose styles for markdown content using shadcn color tokens
- Dark/light theme toggle with localStorage persistence
- Shiki everforest syntax themes for code blocks
- 404 page with VT323 font
- /docs redirect to installation page
- GitHub star count fetch
- Earthy green/cream oklch color palette matching TUI theme

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

website/src/pages/404.astro

@@ -0,0 +1,13 @@
+---
+import Layout from "@/layouts/main.astro"
+---
+
+<Layout title="404 — Feynman">
+  <section class="flex flex-1 items-center justify-center">
+    <div class="flex flex-col items-center gap-4 text-center">
+      <h1 class="font-['VT323'] text-9xl text-primary">404</h1>
+      <p class="text-lg text-muted-foreground">Page not found.</p>
+      <a href="/" class="text-sm text-primary hover:underline">Back to home</a>
+    </div>
+  </section>
+</Layout>