feat: 已离职/解聘员工可重新入职

1. 后端新增 rehireEmployee 函数和 POST /employees/:id/rehire 接口
2. 校验：仅已离职员工可重新入职，新入职日期须晚于上次离职日期
3. 复用员工已有基本信息，只需填写新入职日期和劳动合同
4. 前端花名册已离职员工显示「重新入职」按钮+弹窗（RehireModal）

backend/src/routes/employee.routes.ts

@@ -11,6 +11,7 @@ import {
   getEmployees,
   getEmployeeDetail,
   createEmployee,
+  rehireEmployee,
   updateEmployee,
   deleteEmployee,
   batchRenew,
@@ -64,6 +65,22 @@ router.put('/:id', authMiddleware, async (req: AuthRequest, res, next) => {
   }
 })
 
+router.post('/:id/rehire', authMiddleware, async (req: AuthRequest, res, next) => {
+  try {
+    const result = await rehireEmployee(req.user!.orgId, req.user!.id, req.params.id, req.body)
+    await auditLog(req, 'REHIRE', 'EMPLOYEE', req.params.id, { hireDate: req.body.hireDate })
+    res.json({ success: true, data: result })
+  } catch (err: any) {
+    if (err?.code === 'CONFLICT') {
+      return res.status(409).json({ success: false, error: { code: err.code, message: err.message } })
+    }
+    if (err?.code === 'VALIDATION_ERROR') {
+      return res.status(400).json({ success: false, error: { code: err.code, message: err.message } })
+    }
+    next(err)
+  }
+})
+
 router.delete('/:id', authMiddleware, async (req: AuthRequest, res, next) => {
   try {
     const result = await deleteEmployee(req.user!.orgId, req.params.id)

backend/src/services/contract.service.ts

@@ -203,6 +203,72 @@ export async function createEmployee(orgId: string, userId: string, data: any) {
   return { id: employee.id }
 }
 
+// 重新入职：复用已有员工基本信息，更新入职日期和状态，可选创建新合同
+export async function rehireEmployee(orgId: string, userId: string, id: string, data: any) {
+  const employee = await prisma.employee.findFirst({
+    where: { id, orgId },
+    include: { terminations: { orderBy: { terminationDate: 'desc' }, take: 1 } },
+  })
+  if (!employee) {
+    throw { code: 'NOT_FOUND', message: '员工不存在' }
+  }
+
+  const today = new Date()
+  today.setHours(0, 0, 0, 0)
+  const isResigned = employee.terminations.some((t) => t.terminationDate <= today)
+  if (!isResigned) {
+    throw { code: 'CONFLICT', message: '该员工当前在职，无需重新入职' }
+  }
+
+  const newHireDate = new Date(data.hireDate)
+  const latestTerm = employee.terminations[0]
+  if (latestTerm && newHireDate <= latestTerm.terminationDate) {
+    throw { code: 'VALIDATION_ERROR', message: '新入职日期必须晚于上次离职/解聘日期' }
+  }
+
+  await prisma.employee.update({
+    where: { id },
+    data: {
+      hireDate: newHireDate,
+      status: 'ACTIVE',
+      isPregnant: data.isPregnant || false,
+      isInMedicalPeriod: data.isInMedicalPeriod || false,
+      isWorkInjured: data.isWorkInjured || false,
+    },
+  })
+
+  if (data.contract && data.contract.contractType !== 'UNSIGNED') {
+    const contractMonths = data.contract.endDate
+      ? Math.ceil(daysBetween(new Date(data.contract.endDate), new Date(data.contract.startDate)) / 30.44)
+      : data.contract.contractYears * 12
+
+    const probationCheck = validateProbation(contractMonths, data.contract.probationMonths)
+    if (!probationCheck.valid) {
+      throw { code: 'VALIDATION_ERROR', message: probationCheck.message }
+    }
+
+    await prisma.laborContract.create({
+      data: {
+        orgId,
+        employeeId: id,
+        signDate: data.contract.signDate ? new Date(data.contract.signDate) : null,
+        startDate: new Date(data.contract.startDate),
+        endDate: data.contract.endDate ? new Date(data.contract.endDate) : null,
+        contractType: data.contract.contractType,
+        signMethod: data.contract.signMethod || 'PAPER',
+        contractYears: data.contract.contractYears || 3,
+        probationMonths: data.contract.probationMonths || 0,
+        probationSalary: data.contract.probationSalary || 0,
+        createdBy: userId,
+      },
+    })
+  }
+
+  await runRiskDetection(orgId)
+
+  return { id }
+}
+
 export async function updateEmployee(orgId: string, id: string, data: any) {
   const employee = await prisma.employee.findFirst({ where: { id, orgId } })
   if (!employee) {