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/array-flatten/package.json

@@ -0,0 +1,39 @@
+{
+  "name": "array-flatten",
+  "version": "1.1.1",
+  "description": "Flatten an array of nested arrays into a single flat array",
+  "main": "array-flatten.js",
+  "files": [
+    "array-flatten.js",
+    "LICENSE"
+  ],
+  "scripts": {
+    "test": "istanbul cover _mocha -- -R spec"
+  },
+  "repository": {
+    "type": "git",
+    "url": "git://github.com/blakeembrey/array-flatten.git"
+  },
+  "keywords": [
+    "array",
+    "flatten",
+    "arguments",
+    "depth"
+  ],
+  "author": {
+    "name": "Blake Embrey",
+    "email": "hello@blakeembrey.com",
+    "url": "http://blakeembrey.me"
+  },
+  "license": "MIT",
+  "bugs": {
+    "url": "https://github.com/blakeembrey/array-flatten/issues"
+  },
+  "homepage": "https://github.com/blakeembrey/array-flatten",
+  "devDependencies": {
+    "istanbul": "^0.3.13",
+    "mocha": "^2.2.4",
+    "pre-commit": "^1.0.7",
+    "standard": "^3.7.3"
+  }
+}