feat(admin): redesign navigation with grouped secondary sidebar

Replace flat tabs with categorized navigation groups (Content, Config, etc.).
Update layout styles to support a responsive secondary sidebar.

system-wordings.ts

@@ -443,8 +443,12 @@ export const systemWordingMessages = {
       },
       admin: {
         title: 'Admin',
-        subtitle: 'Maintain system configuration and manage Wiki records.',
+        subtitle: 'Manage Wiki content, configuration, localization, and access.',
         modules: 'Admin modules',
+        contentGroup: 'Content',
+        configurationGroup: 'Configuration',
+        localizationGroup: 'Localization',
+        accessGroup: 'Access',
         loading: 'Loading admin list',
         users: 'Users',
         roles: 'Roles',
@@ -1147,8 +1151,12 @@ export const systemWordingMessages = {
       },
       admin: {
         title: '管理',
-        subtitle: '维护系统配置，查看并删除 Wiki 数据记录。',
+        subtitle: '管理 Wiki 内容、配置、本地化和访问权限。',
         modules: '管理模块',
+        contentGroup: '内容',
+        configurationGroup: '配置',
+        localizationGroup: '本地化',
+        accessGroup: '访问权限',
         loading: '正在加载管理列表',
         users: '用户',
         roles: '角色',