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

webmention-debug.njk

@@ -58,7 +58,7 @@ pagefindIgnore: true
                     <div>{{ legacyUrl }}</div>
                   {% endfor %}
                 {% else %}
-                  <span class="text-surface-400">-</span>
+                  <span class="text-surface-600 dark:text-surface-400">-</span>
                 {% endif %}
               </td>
               <td class="p-2 text-right">
@@ -67,7 +67,7 @@ pagefindIgnore: true
                     {{ allMentions.length }}
                   </span>
                 {% else %}
-                  <span class="text-surface-400">0</span>
+                  <span class="text-surface-600 dark:text-surface-400">0</span>
                 {% endif %}
               </td>
             </tr>