feat(network): 集成ENet库并实现局域网联机对战功能

- 添加ENet库作为网络通信基础，替换原有的原生Socket实现
- 扩展游戏模式支持局域网联机对战（PvP网络模式）
- 重构网络状态结构以适配ENet的Host/Peer模型
- 在图形界面中添加网络对战菜单，支持创建房间和加入房间
- 实现网络消息的发送与接收，包括落子、断开连接等消息类型
- 为网络对战添加定时器轮询机制，实时处理网络事件
- 更新构建系统以编译和链接ENet库

libs/enet/docs/mainpage.dox

@@ -0,0 +1,59 @@
+/** @mainpage ENet
+
+ENet's purpose is to provide a relatively thin, simple and robust
+network communication layer on top of UDP (User Datagram Protocol).
+The primary feature it provides is optional reliable, in-order
+delivery of packets.
+
+ENet omits certain higher level networking features such as authentication, 
+lobbying, server discovery, encryption, or other similar tasks that are
+particularly application specific so that the library remains flexible,
+portable, and easily embeddable.
+
+@ref Features
+
+@ref Downloads
+
+@ref Installation
+
+@ref Tutorial
+
+@ref MailingList
+
+@ref IRCChannel
+
+@ref FAQ
+
+@ref License
+
+<a class="el" href="usergroup0.html">Documentation</a>
+
+ */
+
+/**
+@page Downloads Downloads
+
+You can retrieve the source to ENet by downloading it in either .tar.gz form
+or accessing the github distribution directly.
+
+The most recent stable release (1.3.18) can be downloaded <a class="el" href="download/enet-1.3.18.tar.gz">here</a>.
+The last release that is protocol compatible with the 1.2 series or earlier (1.2.5) can be downloaded <a class="el" href="download/enet-1.2.5.tar.gz">here</a>. 
+
+You can find the most recent ENet source at <a class="el" href="https://github.com/lsalzman/enet">the github repository</a>.
+
+*/
+
+/**
+@page MailingList Mailing List
+
+The <a class="el" href="http://lists.cubik.org/mailman/listinfo/enet-discuss">enet-discuss</a> list is for discussion of ENet, including bug reports or feature requests.
+
+*/
+
+/**
+@page IRCChannel IRC Channel
+
+Join the \#enet channel on the <a class="el" href="https://libera.chat">Libera Chat IRC network (irc.libera.chat)</a> for real-time discussion about the ENet library.
+
+*/
+