fix(socket): 移除 SOCKET_TYPE 引用，修复构建错误

移除了移除 Mock Socket 后遗留的 SOCKET_TYPE 导出引用。

## 修改文件
- src/contexts/NotificationContext.js
  - 删除 SOCKET_TYPE 导入
  - 更新文件注释，删除 Mock/Real 模式说明
  - 简化日志输出，删除 socket 类型显示
  - 移除所有 SOCKET_TYPE 条件判断
  - 统一使用 socket.reconnect?.() 重连逻辑

- src/components/NotificationTestTool/index.js
  - 删除 SOCKET_TYPE 导入
  - Badge 固定显示 "REAL"

## 问题修复
- ✅ 修复构建错误: "SOCKET_TYPE is not exported from '../services/socket'"
- ✅ 简化重连逻辑，不再需要区分 Mock/Real 模式
- ✅ 代码更简洁，移除了 9 处过时引用

## 验证
- npm run build 构建成功
- 无 TypeScript 错误
- 无 import 错误

src/components/NotificationTestTool/index.js

@@ -26,7 +26,6 @@ import {
 } from '@chakra-ui/react';
 import { MdNotifications, MdClose, MdVolumeOff, MdVolumeUp, MdCampaign, MdTrendingUp, MdArticle, MdAssessment, MdWarning } from 'react-icons/md';
 import { useNotification } from '../../contexts/NotificationContext';
-import { SOCKET_TYPE } from '../../services/socket';
 import { NOTIFICATION_TYPES, PRIORITY_LEVELS } from '../../constants/notificationTypes';
 
 const NotificationTestTool = () => {
@@ -295,7 +294,7 @@ const NotificationTestTool = () => {
                     {isConnected ? 'Connected' : 'Disconnected'}
                 </Badge>
                 <Badge colorScheme="purple">
-                    {SOCKET_TYPE}
+                    REAL
                 </Badge>
                 <Badge colorScheme={getPermissionColor()}>
                     浏览器: {getPermissionLabel()}

src/contexts/NotificationContext.js

@@ -2,20 +2,15 @@
 /**
  * 通知上下文 - 管理实时消息推送和通知显示
  *
- * 环境说明：
- * - SOCKET_TYPE === 'REAL': 使用真实 Socket.IO 连接（生产环境），连接到 wss://valuefrontier.cn
- * - SOCKET_TYPE === 'MOCK': 使用模拟 Socket 服务（开发环境），用于本地测试
- *
- * 环境切换：
- * - 设置 REACT_APP_ENABLE_MOCK=true 或 REACT_APP_USE_MOCK_SOCKET=true 使用 MOCK 模式
- * - 否则使用 REAL 模式连接生产环境
+ * 使用真实 Socket.IO 连接到后端服务器
+ * 连接地址配置在环境变量中 (REACT_APP_API_URL)
  */
 
 import React, { createContext, useContext, useState, useEffect, useCallback, useRef } from 'react';
 import { useToast, Box, HStack, Text, Button, CloseButton, VStack, Icon } from '@chakra-ui/react';
 import { BellIcon } from '@chakra-ui/icons';
 import { logger } from '../utils/logger';
-import socket, { SOCKET_TYPE } from '../services/socket';
+import socket from '../services/socket';
 import notificationSound from '../assets/sounds/notification.wav';
 import { browserNotificationService } from '../services/browserNotificationService';
 import { notificationMetricsService } from '../services/notificationMetricsService';
@@ -603,7 +598,7 @@ export const NotificationProvider = ({ children }) => {
     // 连接到 Socket 服务
     useEffect(() => {
         logger.info('NotificationContext', 'Initializing socket connection...');
-        console.log(`%c[NotificationContext] Initializing socket (type: ${SOCKET_TYPE})`, 'color: #673AB7; font-weight: bold;');
+        console.log('%c[NotificationContext] Initializing socket connection', 'color: #673AB7; font-weight: bold;');
 
         // ✅ 第一步: 注册所有事件监听器
         console.log('%c[NotificationContext] Step 1: Registering event listeners...', 'color: #673AB7;');
@@ -665,10 +660,10 @@ export const NotificationProvider = ({ children }) => {
             logger.error('NotificationContext', 'Socket connect_error', error);
             setConnectionStatus(CONNECTION_STATUS.RECONNECTING);
 
-            // 获取重连次数（Real 和 Mock 都支持）
+            // 获取重连次数
             const attempts = socket.getReconnectAttempts?.() || 0;
             setReconnectAttempt(attempts);
-            logger.info('NotificationContext', 'Reconnection attempt', { attempts, socketType: SOCKET_TYPE });
+            logger.info('NotificationContext', 'Reconnection attempt', { attempts });
         });
 
         // 监听重连失败
@@ -798,11 +793,7 @@ export const NotificationProvider = ({ children }) => {
         const handleVisibilityChange = () => {
             if (document.visibilityState === 'visible' && !isConnected && connectionStatus === CONNECTION_STATUS.FAILED) {
                 logger.info('NotificationContext', 'Tab refocused, attempting auto-reconnect');
-                if (SOCKET_TYPE === 'REAL') {
                 socket.reconnect?.();
-                } else {
-                    socket.connect();
-                }
             }
         };
 
@@ -828,11 +819,7 @@ export const NotificationProvider = ({ children }) => {
                     isClosable: true,
                 });
 
-                if (SOCKET_TYPE === 'REAL') {
                 socket.reconnect?.();
-                } else {
-                    socket.connect();
-                }
             }
         };
 
@@ -864,12 +851,7 @@ export const NotificationProvider = ({ children }) => {
     const retryConnection = useCallback(() => {
         logger.info('NotificationContext', 'Manual reconnection triggered');
         setConnectionStatus(CONNECTION_STATUS.RECONNECTING);
-
-        if (SOCKET_TYPE === 'REAL') {
         socket.reconnect?.();
-        } else {
-            socket.connect();
-        }
     }, []);
 
     /**