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/admin/dashboard.html

@@ -38,13 +38,19 @@
     <div class="bg-white rounded-xl shadow-sm border border-gray-200 p-8 text-center">
         <h3 class="text-xl font-semibold text-gray-800 mb-2">{{index .Tr "dash_mgmt_title"}}</h3>
         <p class="text-gray-500 mb-6">{{index .Tr "dash_mgmt_desc"}}</p>
-        <a href="/admin/articles/new"
-            class="inline-flex items-center gap-2 bg-blue-600 text-white px-6 py-3 rounded-lg font-medium hover:bg-blue-700 transition-colors">
-            <svg class="w-5 h-5" fill="none" stroke="currentColor" viewBox="0 0 24 24">
-                <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M12 4v16m8-8H4"/>
-            </svg>
-            {{index .Tr "dash_new_article"}}
-        </a>
+        <div class="flex justify-center gap-3 flex-wrap">
+            <a href="/admin/articles/new"
+                class="inline-flex items-center gap-2 bg-blue-600 text-white px-6 py-3 rounded-lg font-medium hover:bg-blue-700 transition-colors">
+                <svg class="w-5 h-5" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+                    <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M12 4v16m8-8H4"/>
+                </svg>
+                {{index .Tr "dash_new_article"}}
+            </a>
+            <a href="/admin/articles"
+                class="inline-flex items-center gap-2 bg-gray-200 text-gray-700 px-6 py-3 rounded-lg font-medium hover:bg-gray-300 transition-colors">
+                {{index .Tr "article_manage"}}
+            </a>
+        </div>
     </div>
 </section>
 {{template "footer" .}}