Initial commit: Developer Tools MVP with visual editor

- Complete React app with 7 developer tools
- JSON Tool with visual structured editor
- Serialize Tool with visual structured editor
- URL, Base64, CSV/JSON, Beautifier, Diff tools
- Responsive navigation with dropdown menu
- Dark/light mode toggle
- Mobile-responsive design with sticky header
- All tools working with copy/paste functionality

node_modules/underscore/modules/_baseCreate.js

@@ -0,0 +1,18 @@
+import isObject from './isObject.js';
+import { nativeCreate } from './_setup.js';
+
+// Create a naked function reference for surrogate-prototype-swapping.
+function ctor() {
+  return function(){};
+}
+
+// An internal function for creating a new object that inherits from another.
+export default function baseCreate(prototype) {
+  if (!isObject(prototype)) return {};
+  if (nativeCreate) return nativeCreate(prototype);
+  var Ctor = ctor();
+  Ctor.prototype = prototype;
+  var result = new Ctor;
+  Ctor.prototype = null;
+  return result;
+}