feat(website): add site styling updates and SEO improvements

- Update component styling to match Rivet design (FAQ, FeatureGrid, etc.)
- Add SEO improvements (sitemap, robots.txt, meta tags, Open Graph)
- Remove CTASection component
- Update footer tagline
- Add Pi logo

frontend/packages/website/astro.config.mjs

@@ -1,11 +1,14 @@
 import { defineConfig } from 'astro/config';
 import react from '@astrojs/react';
 import tailwind from '@astrojs/tailwind';
+import sitemap from '@astrojs/sitemap';
 
 export default defineConfig({
+  site: 'https://sandbox-agent.dev',
   output: 'static',
   integrations: [
     react(),
-    tailwind()
+    tailwind(),
+    sitemap()
   ]
 });