feat: 转正弹窗显示原薪资 + 薪资变化时联动签署

- ConfirmModal 显示原薪资（¥xxx），转正薪资默认填入原薪资
- 转正薪资与原薪资不同时，提示"将发起薪酬调整确认书签署"
- confirmMutation onSuccess：薪资变化时弹出签署方式选择弹窗
  - scene=POLICY，文件标题为"转正薪酬调整确认书"
  - 备注记录薪资变化：¥原薪资 → ¥新薪资

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

frontend/src/pages/Roster.tsx

@@ -281,13 +281,28 @@ export default function Roster() {
   const confirmMutation = useMutation({
     mutationFn: (data: { employeeId: string; confirmDate: string; regularSalary?: number }) =>
       workProcessApi.create({ type: 'CONFIRM', title: '转正', employeeId: data.employeeId, formData: { employeeId: data.employeeId, confirmDate: data.confirmDate, regularSalary: data.regularSalary }, status: 'DRAFT' }),
-    onSuccess: () => {
+    onSuccess: (_data, variables) => {
       queryClient.invalidateQueries({ queryKey: ['roster'] })
       queryClient.invalidateQueries({ queryKey: ['dashboard'] })
       queryClient.invalidateQueries({ queryKey: ['roster-profile'] })
       setShowConfirmModal(false)
+      const originalSalary = confirmEmployee?.monthlySalary ? Number(confirmEmployee.monthlySalary) : null
+      const newSalary = variables.regularSalary
+      // 薪资有变化时弹出签署方式选择
+      if (newSalary && newSalary !== originalSalary) {
+        setSignChoice({
+          open: true,
+          employeeId: variables.employeeId,
+          employeeName: confirmEmployee?.name || '',
+          scene: 'POLICY',
+          documentTitle: `${confirmEmployee?.name || ''}的转正薪酬调整确认书`,
+          remark: `转正薪资调整：¥${originalSalary || 0} → ¥${newSalary}`,
+          actionName: '转正调薪',
+        })
+      } else {
+        toast.success('转正已提交')
+      }
       setConfirmEmployee(null)
-      toast.success('转正已提交')
     },
     onError: (err: any) => toast.error(err?.response?.data?.error?.message || '转正失败'),
   })