feat: 商业保险/员工福利独立页面+易签宝电子签署框架

- 商业保险：从社公商保中拆出为独立页面，侧边栏新增「福利保障」分组
- 员工福利：新建完整模块（方案管理+批量参保+员工汇总），Prisma模型+后端路由+前端页面
- 电子签署：搭建易签宝对接框架（ESignRecord模型+创建/查询/取消/回调接口+前端签署管理页面）
- 侧边栏新增「福利保障」分组：商业保险、员工福利、电子签署
- Prisma schema 新增6个模型：CommercialInsurancePlan/Enrollment, EmployeeBenefitPlan/Enrollment, ESignRecord

frontend/src/App.tsx

@@ -52,6 +52,9 @@ const OnboardingProgress = lazy(() => import('./pages/portal/OnboardingProgress'
 const ResignationApply = lazy(() => import('./pages/portal/ResignationApply'))
 const RiskCenter = lazy(() => import('./pages/compliance/RiskCenter'))
 const SalaryDashboard = lazy(() => import('./pages/SalaryDashboard'))
+const CommercialInsurance = lazy(() => import('./pages/CommercialInsurance'))
+const EmployeeBenefits = lazy(() => import('./pages/EmployeeBenefits'))
+const ESign = lazy(() => import('./pages/ESign'))
 
 // 平台管理端
 const PlatformLogin = lazy(() => import('./pages/platform/PlatformLogin'))
@@ -198,6 +201,9 @@ export default function App() {
       <Route path="/leave-approval" element={<ProtectedRoute><AdminLayout><LeaveApproval /></AdminLayout></ProtectedRoute>} />
       <Route path="/risk-center" element={<ProtectedRoute><AdminLayout><RiskCenter /></AdminLayout></ProtectedRoute>} />
       <Route path="/salary-dashboard" element={<ProtectedRoute><AdminLayout><SalaryDashboard /></AdminLayout></ProtectedRoute>} />
+      <Route path="/commercial-insurance" element={<ProtectedRoute><AdminLayout><CommercialInsurance /></AdminLayout></ProtectedRoute>} />
+      <Route path="/benefits" element={<ProtectedRoute><AdminLayout><EmployeeBenefits /></AdminLayout></ProtectedRoute>} />
+      <Route path="/esign" element={<ProtectedRoute><AdminLayout><ESign /></AdminLayout></ProtectedRoute>} />
 
       {/* 平台管理端 */}
       <Route path="/platform/login" element={<Suspense fallback={<SkeletonPage />}><PlatformLogin /></Suspense>} />