feat(video): add YouTube lightbox to benefits section

Replaces static video link with a self-contained VideoCard component
that opens a native <dialog> lightbox with autoplay on open and
iframe src teardown on close. Includes pulsing ring animation on the
play button and a rounded-triangle SVG icon.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

www/src/components/VideoCard.astro

@@ -0,0 +1,51 @@
+---
+interface Props {
+  image: string;
+  alt: string;
+  videoUrl: string;
+  videoTitle: string;
+}
+const { image, alt, videoUrl, videoTitle } = Astro.props;
+---
+<button class="video-card" data-video-url={videoUrl} aria-haspopup="dialog" aria-label={`Watch video: ${videoTitle}`}>
+  <img src={`/assets/images/${image}`} alt={alt} />
+  <span aria-hidden="true">
+    <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 50 50" width="50" height="50" fill="currentColor" aria-hidden="true">
+      <path d="M21 12.88L37.5 22.4A3 3 0 0 1 37.5 27.6L21 37.12A3 3 0 0 1 16.5 34.52L16.5 15.48A3 3 0 0 1 21 12.88Z" />
+    </svg>
+  </span>
+</button>
+<dialog class="video-dialog">
+  <div class="video-dialog-inner">
+    <button class="video-dialog-close" aria-label="Close video" autofocus>✕</button>
+    <div class="video-dialog-frame">
+      <iframe title={videoTitle} allowfullscreen allow="autoplay; encrypted-media"></iframe>
+    </div>
+  </div>
+</dialog>
+
+<script>
+  document.querySelectorAll('button.video-card[data-video-url]').forEach((card) => {
+    const dialog = card.nextElementSibling as HTMLDialogElement;
+    const iframe = dialog.querySelector('iframe') as HTMLIFrameElement;
+    const base = card.getAttribute('data-video-url')!;
+    const sep = base.includes('?') ? '&' : '?';
+
+    const closeBtn = dialog.querySelector('.video-dialog-close') as HTMLButtonElement;
+    closeBtn.addEventListener('click', () => dialog.close());
+
+    card.addEventListener('click', () => {
+      iframe.src = `${base}${sep}autoplay=1`;
+      dialog.showModal();
+    });
+
+    dialog.addEventListener('close', () => {
+      iframe.src = '';
+    });
+
+    // Close on backdrop click
+    dialog.addEventListener('click', (e) => {
+      if (e.target === dialog) dialog.close();
+    });
+  });
+</script>