feat(internal): 实现网关服务并优化聊天功能

- 新增 Gateway 结构体和相关方法，用于管理客户端连接和消息分发
- 重构 ChatService，集成 Gateway 功能
- 添加客户端绑定 UID 功能，支持消息发送到指定用户
- 实现全局消息广播和单用户消息发送的 HTTP 接口
- 优化聊天消息处理逻辑，增加消息回显功能

internal/services/chat.go

@@ -81,17 +81,10 @@ func (h *ChatService) Chat(c *websocket.Conn) {
 			break
 		}
 		//简单协议：bind:<uid>
-		if len(message) > 5 && string(message[:5]) == "bind:" {
-			uid := string(message[5:])
+		if c.Headers("Sec-Websocket-Protocol") == "bind" && c.Headers("X-Session") != "" {
+			uid := c.Headers("X-Session")
 			_ = h.Gw.BindUid(clientID, uid)
 			log.Printf("bind %s -> uid:%s\n", clientID, uid)
-			continue
-		}
-		// 回显
-		err = h.Gw.SendToClient(clientID, []byte("echo: "+string(message)))
-		if err != nil {
-			h.ChatFail(c, "send to client failed")
-			continue
 		}
 		msg, chatType := h.handleMessageToString(c, messageType, message)
 		if chatType == constant.ConnStatusClosed {