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/clone.js

@@ -0,0 +1,9 @@
+import isObject from './isObject.js';
+import isArray from './isArray.js';
+import extend from './extend.js';
+
+// Create a (shallow-cloned) duplicate of an object.
+export default function clone(obj) {
+  if (!isObject(obj)) return obj;
+  return isArray(obj) ? obj.slice() : extend({}, obj);
+}