fix: blank_employees 模式不再自动带出基本工资等数据

根因：blank_employees 和 custom 模式共用同一分支，
导致空白员工模式也会自动填充 baseSalary

修复：将 blank_employees 模式单独处理，所有金额默认0

backend/src/routes/payroll2.routes.ts

@@ -524,8 +524,10 @@ router.post('/batches', async (req: AuthRequest, res: Response, next: NextFuncti
         overtimePay = overtime?.totalPay || 0
         allowance = prevPayslip?.allowance || 0
         deduction = prevPayslip?.deduction || 0
-      } else if (mode === 'custom' || mode === 'blank_employees') {
+      } else if (mode === 'blank_employees') {
-        // 自定义/空白员工模式：取员工工资结构（非试用期）
+        // 空白员工模式：拉入员工但所有金额默认0，需手动填写
+      } else if (mode === 'custom') {
+        // 自定义模式：取员工工资结构（非试用期）
         const batchMonthEnd = new Date(`${month}-28T23:59:59`)
         const latestContract = emp.contracts?.[0]
         const inProbation = isInProbation(latestContract, batchMonthEnd)
@@ -535,11 +537,10 @@ router.post('/batches', async (req: AuthRequest, res: Response, next: NextFuncti
         } else if (empBaseSalary > 0 || empPerformanceSalary > 0) {
           baseSalary = empBaseSalary
           // 绩效工资不自动带出，需手动点"获取绩效工资"按钮
-        } else if (emp.monthlySalary && mode === 'custom') {
+        } else if (emp.monthlySalary) {
           // custom 模式旧数据兼容
           try { baseSalary = Number(decrypt(emp.monthlySalary)) || 0 } catch { baseSalary = Number(emp.monthlySalary) || 0 }
         }
-        // blank_employees 模式：金额默认0，不自动带出
       }
       // blank_all: 所有金额默认 0