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/map-iterate.js

@@ -0,0 +1,8 @@
+'use strict';
+var iterateSimple = require('../internals/iterate-simple');
+
+module.exports = function (map, fn, interruptible) {
+  return interruptible ? iterateSimple(map.entries(), function (entry) {
+    return fn(entry[1], entry[0]);
+  }, true) : map.forEach(fn);
+};