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

changelog.njk

@@ -67,7 +67,7 @@ withSidebar: false
                    class="text-xs px-2 py-0.5 rounded-full bg-surface-100 dark:bg-surface-800 text-surface-600 dark:text-surface-400 hover:text-accent-600 dark:hover:text-accent-400"
                    x-text="commit.repoName"></a>
                 <span class="text-xs text-surface-600 dark:text-surface-400 font-mono" x-text="formatDate(commit.date)"></span>
-                <span class="text-xs text-surface-400" x-text="'by ' + commit.author"></span>
+                <span class="text-xs text-surface-600 dark:text-surface-400" x-text="'by ' + commit.author"></span>
               </div>
               <template x-if="commit.body">
                 <details class="mt-2">
@@ -97,7 +97,7 @@ withSidebar: false
     </div>
 
     {# Summary #}
-    <div x-show="commits.length > 0" class="mt-6 text-center text-xs text-surface-400">
+    <div x-show="commits.length > 0" class="mt-6 text-center text-xs text-surface-600 dark:text-surface-400">
       <span x-text="commits.length + ' commits'"></span>
       <span x-show="currentDays !== 'all'"> from the last <span x-text="currentDays"></span> days</span>
       <span x-show="currentDays === 'all'"> (all time)</span>