fix: 修复员工同步统计错误

- create_user 现在返回 (user, status) 元组，区分 created/existing/restored/skipped
- sync_employees 正确统计新增、已存在、恢复、跳过的用户数
- 前端显示更准确的同步结果信息

frontend/src/views/admin/system-settings.vue

@@ -345,11 +345,18 @@ const triggerSync = async () => {
     const response = await request.post('/api/v1/employee-sync/sync')
     if (response.success) {
       const data = response.data
-      ElMessage.success(
-        `同步完成！共处理 ${data.total_employees || 0} 名员工，` +
-        `创建 ${data.users_created || 0} 个账号，` +
-        `跳过 ${data.users_skipped || 0} 个`
-      )
+      const created = data.users_created || 0
+      const existing = data.users_existing || 0
+      const restored = data.users_restored || 0
+      const skipped = data.users_skipped || 0
+      
+      let msg = `同步完成！共处理 ${data.total_employees || 0} 名员工`
+      if (created > 0) msg += `，新增 ${created} 人`
+      if (existing > 0) msg += `，已存在 ${existing} 人`
+      if (restored > 0) msg += `，恢复 ${restored} 人`
+      if (skipped > 0) msg += `，跳过 ${skipped} 人`
+      
+      ElMessage.success(msg)
     } else {
       ElMessage.error(response.message || '同步失败')
     }