fix: 清理AI遗留代码，修复场景配置

- 删除三套旧菜单系统 (MainMenu.cs, MainMenuUI.cs, ModeSelectionUI.cs)
- Ground 添加 BoxCollider 并设置 tag 为 Ground
- UIManager.OnReturnClicked 改为通过 PageController 返回首页
- PageController 增加 ReturnToHome 方法，管理 BtnFixationBack 可见性
- 清理废弃场景 Experiment.unity / ModeSelection.unity 及历史截图

Doc/WebGLBuildSever/node_modules/utils-merge/README.md

@@ -0,0 +1,34 @@
+# utils-merge
+
+[![Version](https://img.shields.io/npm/v/utils-merge.svg?label=version)](https://www.npmjs.com/package/utils-merge)
+[![Build](https://img.shields.io/travis/jaredhanson/utils-merge.svg)](https://travis-ci.org/jaredhanson/utils-merge)
+[![Quality](https://img.shields.io/codeclimate/github/jaredhanson/utils-merge.svg?label=quality)](https://codeclimate.com/github/jaredhanson/utils-merge)
+[![Coverage](https://img.shields.io/coveralls/jaredhanson/utils-merge.svg)](https://coveralls.io/r/jaredhanson/utils-merge)
+[![Dependencies](https://img.shields.io/david/jaredhanson/utils-merge.svg)](https://david-dm.org/jaredhanson/utils-merge)
+
+
+Merges the properties from a source object into a destination object.
+
+## Install
+
+```bash
+$ npm install utils-merge
+```
+
+## Usage
+
+```javascript
+var a = { foo: 'bar' }
+  , b = { bar: 'baz' };
+
+merge(a, b);
+// => { foo: 'bar', bar: 'baz' }
+```
+
+## License
+
+[The MIT License](http://opensource.org/licenses/MIT)
+
+Copyright (c) 2013-2017 Jared Hanson <[http://jaredhanson.net/](http://jaredhanson.net/)>
+
+<a target='_blank' rel='nofollow' href='https://app.codesponsor.io/link/vK9dyjRnnWsMzzJTQ57fRJpH/jaredhanson/utils-merge'>  <img alt='Sponsor' width='888' height='68' src='https://app.codesponsor.io/embed/vK9dyjRnnWsMzzJTQ57fRJpH/jaredhanson/utils-merge.svg' /></a>