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/compose.js

@@ -0,0 +1,14 @@
+// Returns a function that is the composition of a list of functions, each
+// consuming the return value of the function that follows.
+function compose() {
+  var args = arguments;
+  var start = args.length - 1;
+  return function() {
+    var i = start;
+    var result = args[start].apply(this, arguments);
+    while (i--) result = args[i].call(this, result);
+    return result;
+  };
+}
+
+module.exports = compose;