fix: 线下签署登记标题英文转中文+完成时间时区+签署记录角标

1. documentTitle 中 contractType 枚举值转中文
   （LABOR→劳务协议、FIXED→固定期限劳动合同等）
2. 签署日期解析改为本地时区构造（new Date(y,m-1,d,12)），
   避免 new Date('2026-08-16') 被解析为 UTC 00:00 导致
   本地 +8 显示为 08:00:00
3. 签署记录 Tab 增加数字角标显示总记录数

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frontend/src/components/layout/SidebarNav.tsx

@@ -16,6 +16,7 @@ import {
   ChevronDown, ChevronRight,
   Building2, CalendarDays, ClipboardList, Heart, CalendarClock,
   Gift, PenTool, Umbrella, GraduationCap, TrendingUp, AlertTriangle,
+  DollarSign,
 } from 'lucide-react'
 import Logo from '../ui/Logo'
 import { settingsApi } from '../../lib/api-services'
@@ -50,6 +51,7 @@ const navGroups: NavGroup[] = [
       { path: '/performance-records', label: '绩效考核', icon: TrendingUp },
       { path: '/disciplinary-records', label: '违纪记录', icon: AlertTriangle },
       { path: '/special-status', label: '特殊员工', icon: Heart },
+      { path: '/commission-bonus', label: '提成奖金', icon: DollarSign },
     ],
   },
   {