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/amd/value.js

@@ -0,0 +1,13 @@
+define(function () {
+
+  // Extract the result from a wrapped (and possibly chained) object.
+  // This function is also aliased as `valueOf` and `toJSON`, which provide
+  // unwrapping proxies for some methods used in engine operations such as
+  // arithmetic and JSON stringification.
+  function value(wrapper) {
+    return wrapper._wrapped || wrapper;
+  }
+
+  return value;
+
+});