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/inherits/inherits_browser.js

@@ -0,0 +1,27 @@
+if (typeof Object.create === 'function') {
+  // implementation from standard node.js 'util' module
+  module.exports = function inherits(ctor, superCtor) {
+    if (superCtor) {
+      ctor.super_ = superCtor
+      ctor.prototype = Object.create(superCtor.prototype, {
+        constructor: {
+          value: ctor,
+          enumerable: false,
+          writable: true,
+          configurable: true
+        }
+      })
+    }
+  };
+} else {
+  // old school shim for old browsers
+  module.exports = function inherits(ctor, superCtor) {
+    if (superCtor) {
+      ctor.super_ = superCtor
+      var TempCtor = function () {}
+      TempCtor.prototype = superCtor.prototype
+      ctor.prototype = new TempCtor()
+      ctor.prototype.constructor = ctor
+    }
+  }
+}