fix: resolve E2E test failures

- nav: replace hidden newsletter form + Subscribe link with visible inline form
- nav: fix theme toggle aria-label to 'Toggle theme' (was 'Toggle Dark Mode')
- article_page: wrap share buttons in <section aria-label='Share this article'>

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

templates/blog/article_page.html

@@ -69,7 +69,7 @@
     <div class="sticky top-28">
 
       <!-- Share -->
-      <div class="mb-8">
+      <section aria-label="Share this article" class="mb-8">
         <h3 class="font-display font-bold text-lg mb-4 uppercase tracking-widest text-zinc-500 text-sm">Share Article</h3>
         <div class="flex gap-2">
           <a href="https://x.com/intent/post?url={{ request.build_absolute_uri|urlencode }}&text={{ page.title|urlencode }}" target="_blank" rel="noopener noreferrer"
@@ -85,7 +85,7 @@
             <svg class="w-4 h-4" xmlns="http://www.w3.org/2000/svg" fill="none" viewBox="0 0 24 24" stroke-width="2" stroke="currentColor"><path stroke-linecap="round" stroke-linejoin="round" d="M13.19 8.688a4.5 4.5 0 0 1 1.242 7.244l-4.5 4.5a4.5 4.5 0 0 1-6.364-6.364l1.757-1.757m13.35-.622 1.757-1.757a4.5 4.5 0 0 0-6.364-6.364l-4.5 4.5a4.5 4.5 0 0 0 1.242 7.244" /></svg>
           </button>
         </div>
-      </div>
+      </section>
 
       <!-- Newsletter -->
       <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">