fix: prevent overlapping speech synthesis playback

--bug=1058747 --user=刘瑞斌 【应用】应用开启语音播放自动播放，使用移动端提问后没有自动播放 https://www.tapd.cn/62980211/s/1731646

ui/src/components/ai-chat/component/operation-button/ChatOperationButton.vue

@@ -474,6 +474,9 @@ class AudioManage {
         }
         // 等待取消完成后重新播放
         setTimeout(() => {
+          if (speechSynthesis.speaking) {
+            return
+          }
           speechSynthesis.speak(audioElement)
           this.statusList[index] = AudioStatus.PLAY_INT
         }, 500)