feat: 添加游戏启动界面和着色器效果

- 新增启动界面背景和logo
- 实现顶部和底部阴影着色器
- 添加难度选择滑块和角色名输入框
- 优化多人游戏按钮交互
- 修复编译提示面板的动画效果
- 更新UI主题样式

resources/ui/slider.svg

@@ -0,0 +1 @@
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