feat: add role-based access control and user article management

- Add AdminRequired middleware to all /admin routes for proper authorization
- Restrict admin panel, comments, users, settings to admin role only
- Create separate /my/articles routes for regular users to manage their own articles
- Add MyArticlesPage handler for users to view/edit/delete their own content
- Update navigation menus with role-based visibility
- Admin dropdown shows only 'Admin Panel' link, other features in dashboard
- Regular users see 'My Articles' link in profile dropdown
- Add i18n translations for 'my_articles' and 'comment_manage' keys
- Fix permission boundary issues where author role could access admin settings

Security improvements:
- Platform settings now require admin role
- Comment moderation requires admin role
- User management requires admin role
- Regular users can only manage their own articles

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

templates/admin/dashboard.html

@@ -55,11 +55,15 @@
                 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 "dash_user_mgmt"}}
             </a>
-            {{end}}
+            <a href="/admin/comments"
+                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 "comment_manage"}}
+            </a>
             <a href="/admin/settings/site"
                 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 "settings_nav"}}
             </a>
+            {{end}}
         </div>
     </div>
 </section>