perf: address PageSpeed Insights issues (CLS, contrast, touch targets, JS minification)

- Reserve sidebar min-height on desktop to prevent CLS from Alpine.js hydration
- Defer lite-yt-embed.css with media="print" onload pattern
- Add terser JS minification in eleventy.after build hook
- Increase touch target sizing for category pills, facepile avatars, nav items
- Fix text-surface-400 contrast ratio (3.05:1 → 6.23:1) across 20 instances

Confab-Link: http://localhost:8080/sessions/edb1b7b0-da66-4486-bd9c-d1cfa7553b88

lib/unfurl-shortcode.js

@@ -110,7 +110,7 @@ export function renderCard(url, metadata) {
     <div class="flex-1 p-3 sm:p-4 min-w-0">
       <p class="font-semibold text-sm sm:text-base text-surface-900 dark:text-surface-100 truncate m-0">${escapeHtml(title)}</p>
       ${desc ? `<p class="text-xs sm:text-sm text-surface-600 dark:text-surface-400 mt-1 m-0 line-clamp-2">${escapeHtml(desc)}</p>` : ""}
-      <p class="text-xs text-surface-400 dark:text-surface-400 mt-2 m-0">${faviconHtml}${escapeHtml(domain)}</p>
+      <p class="text-xs text-surface-600 dark:text-surface-400 mt-2 m-0">${faviconHtml}${escapeHtml(domain)}</p>
     </div>
     ${imgHtml}
   </a>