fix: portal端token过期后自动跳转登录页，避免显示空数据

- portalAxios 401 响应拦截器：清除 token 并跳转 /portal/login
- PortalLayoutWrapper：检查 token 是否存在，不存在则跳转登录页
- 排除 /portal/login 和 /portal/auto-login 页面避免重复跳转

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frontend/src/components/layout/SidebarNav.tsx

@@ -16,7 +16,7 @@ import {
   ChevronDown, ChevronRight,
   Building2, CalendarDays, ClipboardList, Heart, CalendarClock,
   Gift, PenTool, Umbrella, GraduationCap, TrendingUp, AlertTriangle,
-  DollarSign,
+  DollarSign, Clock,
 } from 'lucide-react'
 import { settingsApi } from '../../lib/api-services'
 
@@ -64,6 +64,7 @@ const navGroups: NavGroup[] = [
     items: [
       { path: '/money', label: '薪税管理', icon: Calculator },
       { path: '/social', label: '社保公积金', icon: Shield },
+      { path: '/overtime', label: '加班费计算', icon: Clock },
       { path: '/commission-bonus', label: '提成奖金', icon: DollarSign },
       { path: '/salary-dashboard', label: '薪酬分析', icon: BarChart3 },
     ],