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/cjs/_bindCb.js

@@ -0,0 +1,10 @@
+// Internal function that returns a bound version of the passed-in callback, to
+// be repeatedly applied in other Underscore functions.
+function bindCb(func, context) {
+  if (context === void 0) return func;
+  return function() {
+    return func.apply(context, arguments);
+  };
+}
+
+module.exports = bindCb;