feat: 电子签署导航调整+员工手机端电子签署功能

- 管理端导航：电子签署移到首页分组（工作日历下）
- 员工端新增电子签署页面（MyEsign.tsx）：
  - 查看自己的签署记录列表，支持待签/已签/已取消状态
  - 查看签署详情，含文件内容、关联合同标识
  - 确认签署操作（框架阶段，对接易签宝后跳转签署页面）
- 员工端导航（PortalNav）增加电子签署入口
- 员工首页（EmployeeHome）增加电子签署快捷入口
- 员工首页待办事项增加待签署文件提醒
- 后端portal路由新增3个接口：GET /esign、GET /esign/:id、POST /esign/:id/sign

frontend/src/App.tsx

@@ -50,6 +50,7 @@ const LeaveApproval = lazy(() => import('./pages/LeaveApproval'))
 const EmployeeHome = lazy(() => import('./pages/portal/EmployeeHome'))
 const OnboardingProgress = lazy(() => import('./pages/portal/OnboardingProgress'))
 const ResignationApply = lazy(() => import('./pages/portal/ResignationApply'))
+const MyEsign = lazy(() => import('./pages/portal/MyEsign'))
 const RiskCenter = lazy(() => import('./pages/compliance/RiskCenter'))
 const SalaryDashboard = lazy(() => import('./pages/SalaryDashboard'))
 const CommercialInsurance = lazy(() => import('./pages/CommercialInsurance'))
@@ -224,6 +225,7 @@ export default function App() {
       <Route path="/portal/home" element={<PortalLayoutWrapper><EmployeeHome /></PortalLayoutWrapper>} />
       <Route path="/portal/onboarding-progress" element={<PortalLayoutWrapper><OnboardingProgress /></PortalLayoutWrapper>} />
       <Route path="/portal/resignation" element={<PortalLayoutWrapper><ResignationApply /></PortalLayoutWrapper>} />
+      <Route path="/portal/esign" element={<PortalLayoutWrapper><MyEsign /></PortalLayoutWrapper>} />
 
       {/* 兜底 */}
       <Route path="*" element={<Navigate to="/" replace />} />