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/internals/a-weak-key.js

@@ -0,0 +1,12 @@
+'use strict';
+var WeakMapHelpers = require('../internals/weak-map-helpers');
+
+var weakmap = new WeakMapHelpers.WeakMap();
+var set = WeakMapHelpers.set;
+var remove = WeakMapHelpers.remove;
+
+module.exports = function (key) {
+  set(weakmap, key, 1);
+  remove(weakmap, key);
+  return key;
+};