feat(alert-center): 添加飞书Webhook通知渠道 + 告警引擎实时通知

- 后端: NotifyChannel 模型新增 feishu 类型, FeishuWebhookConfig
- 后端: TestNotifyChannel 真实发送飞书测试消息(文本格式)
- 后端: 告警引擎触发/恢复时自动发送飞书通知(sendFeishuAlert/sendFeishuRecovery)
- 后端: AlertEngine 新增 tcp_time_wait/tcp_close_wait/service_process 指标检测
- 后端: NetworkStatModel 新增 TCPCloseWait 字段
- 后端: QuickSetupRules 一键创建6条告警规则(CPU/内存/磁盘/TIME_WAIT/CLOSE_WAIT/进程)
- 后端: 注册 /alerts/quick-setup 路由
- 前端: AlertChannelDialog 新增飞书类型选项
- 前端: helpers 新增 getChannelIcon/getChannelTypeLabel 支持 feishu/dingtalk/wechat

backend/internal/api/handlers/pipeline_executor.go

@@ -566,7 +566,7 @@ var (
 // 否则 → 加入队列 (status=queued)
 func (h *PipelineHandler) tryExecuteOrQueue(pipeline models.Pipeline, run models.PipelineRun) {
 	max := pipeline.MaxExecutors
-	if max <= 0 { max = 1 }
+	if max <= 0 { max = 2 }
 
 	queueMu.Lock()
 	running := pipelineRunningCount[pipeline.ID]