fix(pipeline): BREAK-04 接入 pipeline-complete 事件监听

PipelinesPanel 新增 useEffect 订阅 PipelineClient.onComplete()，
处理用户导航离开后的后台 Pipeline 完成通知。

- 后台完成时 toast 提示成功/失败
- 跳过当前选中 pipeline 的重复通知（轮询路径已处理）
- 组件卸载时自动清理监听器

desktop/src/components/PipelinesPanel.tsx

@@ -7,7 +7,7 @@
  * Pipelines orchestrate Skills and Hands to accomplish complex tasks.
  */
 
-import { useState } from 'react';
+import { useState, useEffect } from 'react';
 import {
   Play,
   RefreshCw,
@@ -437,6 +437,22 @@ export function PipelinesPanel() {
   const [runResult, setRunResult] = useState<{ result: PipelineRunResponse; pipeline: PipelineInfo } | null>(null);
   const { toast } = useToast();
 
+  // Subscribe to pipeline-complete push events (for background completion)
+  useEffect(() => {
+    let unlisten: (() => void) | undefined;
+    PipelineClient.onComplete((event) => {
+      // Only show notification if we're not already tracking this run
+      // (the polling path handles in-flight runs via handleRunComplete)
+      if (selectedPipeline?.id === event.pipelineId) return;
+      if (event.status === 'completed') {
+        toast(`Pipeline "${event.pipelineId}" 后台执行完成`, 'success');
+      } else if (event.status === 'failed') {
+        toast(`Pipeline "${event.pipelineId}" 后台执行失败: ${event.error ?? ''}`, 'error');
+      }
+    }).then((fn) => { unlisten = fn; });
+    return () => { unlisten?.(); };
+  }, [selectedPipeline, toast]);
+
   // Fetch all pipelines without filtering
   const { pipelines, loading, error, refresh } = usePipelines({});