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/core-js-pure/internals/async-iterator-indexed.js

@@ -0,0 +1,13 @@
+'use strict';
+var call = require('../internals/function-call');
+var map = require('../internals/async-iterator-map');
+
+var callback = function (value, counter) {
+  return [counter, value];
+};
+
+// `AsyncIterator.prototype.indexed` method
+// https://github.com/tc39/proposal-iterator-helpers
+module.exports = function indexed() {
+  return call(map, this, callback);
+};