fix: 全面优化安全、性能和代码质量

P0: 环境变量校验/事务保护/RBAC权限
P1: 花名册分页/密码重置验证码/ErrorBoundary/N+1查询优化
P2: 导出限制/自定义错误类/body大小限制/代码去重
P3: 自定义确认弹窗替换window.confirm

backend/src/routes/employee.routes.ts

@@ -111,22 +111,30 @@ router.post('/contracts/preview-renew', authMiddleware, async (req: AuthRequest,
     }
 
     // 合规检查：按员工分组，检查历史固定期合同次数
+    const employeeIds = contracts.map((c) => c.employeeId)
+    const allFixedContracts = await prisma.laborContract.findMany({
+      where: {
+        employeeId: { in: employeeIds },
+        orgId: req.user!.orgId,
+        contractType: 'FIXED',
+      },
+      orderBy: { startDate: 'asc' },
+    })
+    const fixedContractsByEmp = new Map<string, typeof allFixedContracts>()
+    for (const c of allFixedContracts) {
+      if (!fixedContractsByEmp.has(c.employeeId)) {
+        fixedContractsByEmp.set(c.employeeId, [])
+      }
+      fixedContractsByEmp.get(c.employeeId)!.push(c)
+    }
+
     const results = []
     for (const contract of contracts) {
       const employee = contract.employee
-
-      // 查找该员工所有历史固定期合同（按时间正序，用于判断续签次数）
-      const allFixedContracts = await prisma.laborContract.findMany({
-        where: {
-          employeeId: contract.employeeId,
-          orgId: req.user!.orgId,
-          contractType: 'FIXED',
-        },
-        orderBy: { startDate: 'asc' },
-      })
+      const empFixedContracts = fixedContractsByEmp.get(contract.employeeId) || []
 
       // 当前合同是第几次固定期（从1开始计数）
-      const currentIndex = allFixedContracts.findIndex((c) => c.id === contract.id)
+      const currentIndex = empFixedContracts.findIndex((c) => c.id === contract.id)
       const renewalCount = currentIndex + 1
 
       // 判断是否应签无固定期限：