fix(web): 修复普通流式发送时用户消息延迟显示

在 legacy 流式发送路径中补齐本地乐观用户消息，避免消息发送后等待历史刷新才出现在对话中。

web/src/components/AgentChatComponent.vue

@@ -1412,6 +1412,12 @@ const handleSendMessage = async ({ image } = {}) => {
 
   threadState.isStreaming = true
   resetOnGoingConv(threadId)
+  const requestId = createClientRequestId()
+  insertOptimisticHumanMessage(threadState, {
+    requestId,
+    text,
+    imageContent
+  })
   threadState.streamAbortController = new AbortController()
 
   try {