feat: 添加流式响应支持

## 新增功能
1. **流式聊天控制器**: StreamingAIChatController.java
   - 支持SSE (Server-Sent Events) 流式响应
   - 添加/chat/stream端点用于流式聊天
   - 添加/chat/stream/test端点用于测试
   - 添加/chat/compatible兼容端点

2. **前端流式支持**:
   - 更新frontend-config.js添加流式端点配置
   - 更新前端HTML支持流式响应显示
   - 添加打字指示器和流式文本动画
   - 实现流式响应回退机制

3. **技术特性**:
   - 使用HttpURLConnection处理流式HTTP请求
   - 实现SSE事件流解析
   - 支持实时文本逐字显示
   - 保持向后兼容性

## 端点说明
-  - 流式聊天 (SSE)
-  - 流式测试
-  - 兼容端点
- 原有端点保持不变，确保向后兼容

## 前端改进
- 实时显示AI回复过程
- 添加打字动画效果
- 流式响应失败时自动回退
- 优化用户体验

Author: zyh616598128

frontend-config.js

@@ -2,7 +2,10 @@
 const config = {
   API_BASE_URL: process.env.REACT_APP_API_URL || 'http://81.70.234.241:8080/api/v1',
   ENDPOINTS: {
-    CHAT: '/chat/text',
+    CHAT: '/chat/text',           // 非流式聊天
+    CHAT_STREAM: '/chat/stream',   // 流式聊天
+    CHAT_COMPATIBLE: '/chat/compatible', // 兼容端点
+    CHAT_TEST: '/chat/stream/test', // 流式测试
     PING: '/ping',
     STATUS: '/status',
     ECHO: '/echo'
@@ -14,7 +17,87 @@ const getApiUrl = (endpoint) => {
   return `${config.API_BASE_URL}${config.ENDPOINTS[endpoint] || endpoint}`;
 };
 
+// 流式响应处理器
+class StreamHandler {
+  constructor(options = {}) {
+    this.onChunk = options.onChunk || (() => {});
+    this.onComplete = options.onComplete || (() => {});
+    this.onError = options.onError || (() => {});
+    this.fullResponse = '';
+  }
+
+  // 处理SSE流
+  async processStream(url, data) {
+    try {
+      const response = await fetch(url, {
+        method: 'POST',
+        headers: {
+          'Content-Type': 'application/json',
+        },
+        body: JSON.stringify(data)
+      });
+
+      if (!response.ok) {
+        throw new Error(`HTTP error! status: ${response.status}`);
+      }
+
+      const reader = response.body.getReader();
+      const decoder = new TextDecoder('utf-8');
+      let buffer = '';
+
+      while (true) {
+        const { done, value } = await reader.read();
+        
+        if (done) {
+          this.onComplete(this.fullResponse);
+          break;
+        }
+
+        buffer += decoder.decode(value, { stream: true });
+        const lines = buffer.split('\n');
+        buffer = lines.pop() || '';
+
+        for (const line of lines) {
+          if (line.startsWith('data: ')) {
+            const dataStr = line.substring(6);
+            
+            if (dataStr === '[DONE]') {
+              this.onComplete(this.fullResponse);
+              return;
+            }
+
+            try {
+              const eventData = JSON.parse(dataStr);
+              
+              if (eventData.chunk) {
+                this.fullResponse += eventData.chunk;
+                this.onChunk(eventData.chunk, this.fullResponse, eventData);
+              } else if (eventData.error) {
+                this.onError(eventData.error);
+              } else if (eventData.complete) {
+                this.onComplete(this.fullResponse);
+              }
+            } catch (e) {
+              console.warn('解析流式数据失败:', e, dataStr);
+            }
+          }
+        }
+      }
+    } catch (error) {
+      this.onError(error.message);
+    }
+  }
+
+  // 简单的流式请求
+  static async simpleStream(url, data, onChunk) {
+    const handler = new StreamHandler({ onChunk });
+    await handler.processStream(url, data);
+    return handler.fullResponse;
+  }
+}
+
 export default {
   ...config,
-  getApiUrl
+  getApiUrl,
+  StreamHandler
 };