修复任务服务中的 groupMode 赋值逻辑，确保在未定义时使用系统配置的默认值

src/task/task.service.ts

@@ -142,7 +142,7 @@ export class TaskService implements OnModuleInit {
         task.message = task.message || ''
         task.total = phones.length
         task.country = phoneList.country
-        task.groupMode = await this.sysConfigService.getBoolean('group_mode', false)
+        task.groupMode = task.groupMode ?? await this.sysConfigService.getBoolean('group_mode', false)
         if (task.country) {
             const countryConfig = await this.countryConfigService.getDestConfig(task.country)
             task.useBackup = countryConfig.useBackup