fix(ai): harden SSE stream error handling

- make chat SSE timeout configurable and default to 10 minutes

- stop upstream stream client when emitter send fails

- add full exception logging and frontend error notification on stream failures

easyflow-starter/easyflow-starter-all/src/main/resources/application.yml

@@ -70,6 +70,9 @@ spring:
       enabled: true
 
 easyflow:
+  chat:
+    # SSE 超时时间（毫秒），默认 10 分钟，可按需调整
+    sse-timeout-ms: 600000
   # 语音播放、识别服务（阿里云）
   audio:
     type: aliAudioService