refactor: 移除SocketIOClient并更新认证场景

- 移除SocketIOClient.gd及.uid文件
- 更新ChatManager以适配新的架构
- 添加认证UI图片资源和背景音乐
- 优化AuthScene布局和配置
- 更新MainScene和项目配置

project.godot

@@ -33,7 +33,7 @@ gdscript/warnings/treat_warnings_as_errors=false
 window/size/viewport_width=1920
 window/size/viewport_height=1080
 window/size/mode=2
-window/stretch/mode="viewport"
+window/stretch/mode="canvas_items"
 window/stretch/aspect="expand"
 
 [gui]