feat: 添加简单模式功能

新增简单模式设置，适合个人使用场景：
- 隐藏多用户管理相关菜单（用户管理、兑换码等）
- 自动关闭用户注册功能
- 管理员并发数自动设为无限制(99999)
- 侧边栏根据模式动态调整菜单项

同时优化分组页面的"专属分组"功能，添加帮助提示说明使用场景

frontend/src/components/layout/AppSidebar.vue

@@ -45,8 +45,8 @@
           </router-link>
         </div>
 
-        <!-- Personal Section for Admin -->
-        <div class="sidebar-section">
+        <!-- Personal Section for Admin (hidden in simple mode) -->
+        <div v-if="!simpleMode" class="sidebar-section">
           <div v-if="!sidebarCollapsed" class="sidebar-section-title">
             {{ t('nav.myAccount') }}
           </div>
@@ -154,6 +154,7 @@ const isDark = ref(document.documentElement.classList.contains('dark'))
 const siteName = computed(() => appStore.siteName)
 const siteLogo = computed(() => appStore.siteLogo)
 const siteVersion = computed(() => appStore.siteVersion)
+const simpleMode = computed(() => appStore.simpleMode)
 
 // SVG Icon Components
 const DashboardIcon = {
@@ -402,36 +403,54 @@ const ChevronDoubleRightIcon = {
 }
 
 // User navigation items (for regular users)
-const userNavItems = computed(() => [
-  { path: '/dashboard', label: t('nav.dashboard'), icon: DashboardIcon },
-  { path: '/keys', label: t('nav.apiKeys'), icon: KeyIcon },
-  { path: '/usage', label: t('nav.usage'), icon: ChartIcon },
-  { path: '/subscriptions', label: t('nav.mySubscriptions'), icon: CreditCardIcon },
-  { path: '/redeem', label: t('nav.redeem'), icon: GiftIcon },
-  { path: '/profile', label: t('nav.profile'), icon: UserIcon }
-])
+const userNavItems = computed(() => {
+  const items = [
+    { path: '/dashboard', label: t('nav.dashboard'), icon: DashboardIcon },
+    { path: '/keys', label: t('nav.apiKeys'), icon: KeyIcon },
+    { path: '/usage', label: t('nav.usage'), icon: ChartIcon, hideInSimpleMode: true },
+    { path: '/subscriptions', label: t('nav.mySubscriptions'), icon: CreditCardIcon, hideInSimpleMode: true },
+    { path: '/redeem', label: t('nav.redeem'), icon: GiftIcon, hideInSimpleMode: true },
+    { path: '/profile', label: t('nav.profile'), icon: UserIcon }
+  ]
+  return simpleMode.value ? items.filter(item => !item.hideInSimpleMode) : items
+})
 
 // Personal navigation items (for admin's "My Account" section, without Dashboard)
-const personalNavItems = computed(() => [
-  { path: '/keys', label: t('nav.apiKeys'), icon: KeyIcon },
-  { path: '/usage', label: t('nav.usage'), icon: ChartIcon },
-  { path: '/subscriptions', label: t('nav.mySubscriptions'), icon: CreditCardIcon },
-  { path: '/redeem', label: t('nav.redeem'), icon: GiftIcon },
-  { path: '/profile', label: t('nav.profile'), icon: UserIcon }
-])
+const personalNavItems = computed(() => {
+  const items = [
+    { path: '/keys', label: t('nav.apiKeys'), icon: KeyIcon },
+    { path: '/usage', label: t('nav.usage'), icon: ChartIcon, hideInSimpleMode: true },
+    { path: '/subscriptions', label: t('nav.mySubscriptions'), icon: CreditCardIcon, hideInSimpleMode: true },
+    { path: '/redeem', label: t('nav.redeem'), icon: GiftIcon, hideInSimpleMode: true },
+    { path: '/profile', label: t('nav.profile'), icon: UserIcon }
+  ]
+  return simpleMode.value ? items.filter(item => !item.hideInSimpleMode) : items
+})
 
 // Admin navigation items
-const adminNavItems = computed(() => [
-  { path: '/admin/dashboard', label: t('nav.dashboard'), icon: DashboardIcon },
-  { path: '/admin/users', label: t('nav.users'), icon: UsersIcon },
-  { path: '/admin/groups', label: t('nav.groups'), icon: FolderIcon },
-  { path: '/admin/subscriptions', label: t('nav.subscriptions'), icon: CreditCardIcon },
-  { path: '/admin/accounts', label: t('nav.accounts'), icon: GlobeIcon },
-  { path: '/admin/proxies', label: t('nav.proxies'), icon: ServerIcon },
-  { path: '/admin/redeem', label: t('nav.redeemCodes'), icon: TicketIcon },
-  { path: '/admin/usage', label: t('nav.usage'), icon: ChartIcon },
-  { path: '/admin/settings', label: t('nav.settings'), icon: CogIcon }
-])
+const adminNavItems = computed(() => {
+  const baseItems = [
+    { path: '/admin/dashboard', label: t('nav.dashboard'), icon: DashboardIcon },
+    { path: '/admin/users', label: t('nav.users'), icon: UsersIcon, hideInSimpleMode: true },
+    { path: '/admin/groups', label: t('nav.groups'), icon: FolderIcon },
+    { path: '/admin/subscriptions', label: t('nav.subscriptions'), icon: CreditCardIcon },
+    { path: '/admin/accounts', label: t('nav.accounts'), icon: GlobeIcon },
+    { path: '/admin/proxies', label: t('nav.proxies'), icon: ServerIcon },
+    { path: '/admin/redeem', label: t('nav.redeemCodes'), icon: TicketIcon, hideInSimpleMode: true },
+    { path: '/admin/usage', label: t('nav.usage'), icon: ChartIcon },
+  ]
+
+  // 简单模式下，在系统设置前插入 API密钥
+  if (simpleMode.value) {
+    const filtered = baseItems.filter(item => !item.hideInSimpleMode)
+    filtered.push({ path: '/keys', label: t('nav.apiKeys'), icon: KeyIcon })
+    filtered.push({ path: '/admin/settings', label: t('nav.settings'), icon: CogIcon })
+    return filtered
+  }
+
+  baseItems.push({ path: '/admin/settings', label: t('nav.settings'), icon: CogIcon })
+  return baseItems
+})
 
 function toggleSidebar() {
   appStore.toggleSidebar()