feat(site): show the desktop demo in the hero and README

site/home.js

@@ -0,0 +1,18 @@
+const demo = document.querySelector('#desktop-demo');
+const reducedMotion = window.matchMedia('(prefers-reduced-motion: reduce)');
+let started = false;
+
+// Start muted when the demo comes into view. Native controls remain available
+// without JavaScript and after a visitor pauses playback.
+const visibility = new IntersectionObserver(([entry]) => {
+  if (!entry.isIntersecting) {
+    demo.pause();
+  } else if (!started && !reducedMotion.matches) {
+    started = true;
+    demo.play().catch(() => {});
+  }
+}, { threshold: 0.25 });
+visibility.observe(demo);
+reducedMotion.addEventListener('change', () => {
+  if (reducedMotion.matches) demo.pause();
+});