feat: add article management (list, edit, delete)

- Add admin article list page at /admin/articles with status badges,
  pin marker, publish time, and edit/delete actions
- Share the create/edit form: dynamic action URL, prefilled fields,
  is_top checkbox state, and create-vs-edit heading
- Add ArticleUpdate/ArticleDelete handlers (soft-delete via DeletedAt);
  stamp PublishedAt on first publish
- Add "Manage Articles" entry on the dashboard
- Hide home page sign-in/dashboard buttons
- Add EN/ZH i18n keys for the management UI

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

templates/pages/home.html

@@ -7,14 +7,14 @@
     <p class="text-xl text-gray-600 mb-8 max-w-2xl mx-auto">
         {{index .Tr "home_subtitle"}}
     </p>
-    <div class="flex justify-center gap-4">
+    <!-- <div class="flex justify-center gap-4">
         <a href="/login" class="inline-block bg-blue-600 text-white px-6 py-3 rounded-lg font-medium hover:bg-blue-700 transition-colors">
             {{index .Tr "home_sign_in"}}
         </a>
         <a href="/admin" class="inline-block bg-gray-200 text-gray-700 px-6 py-3 rounded-lg font-medium hover:bg-gray-300 transition-colors">
             {{index .Tr "home_to_dash"}}
         </a>
-    </div>
+    </div> -->
 </section>
 
 <section class="max-w-5xl mx-auto px-4 py-16">