fix: address code review issues and rebuild CSS

- nav: add functional mobile menu panel with JS toggle
- nav: hamburger now shows/hides mobile-menu with aria-expanded state
- about_page: full styled layout (header, prose body, author aside)
- legal_page: full styled layout (header with last-updated, max-w-3xl prose)
- article: fix aside newsletter label to 'Subscribe' for E2E test
- CSS: rebuild after all template changes (4.8KB → 24.3KB)
  Committed CSS must match CI build — rebuilt after ALL template edits

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

templates/blog/article_page.html

@@ -91,7 +91,7 @@
       <div class="bg-brand-dark text-brand-light dark:bg-brand-light dark:text-brand-dark p-6 border border-transparent dark:border-zinc-700 shadow-solid-dark dark:shadow-solid-light">
         <h3 class="font-display font-bold text-xl mb-2">Subscribe for Updates</h3>
         <p class="text-sm opacity-80 mb-4">Get our latest articles and coding benchmarks delivered to your inbox every week.</p>
-        {% include 'components/newsletter_form.html' with source='article' label='Never miss a post' %}
+        {% include 'components/newsletter_form.html' with source='article' label='Subscribe' %}
       </div>
 
     </div>