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/modules/web.url.to-json.js

@@ -0,0 +1,11 @@
+'use strict';
+var $ = require('../internals/export');
+var call = require('../internals/function-call');
+
+// `URL.prototype.toJSON` method
+// https://url.spec.whatwg.org/#dom-url-tojson
+$({ target: 'URL', proto: true, enumerable: true }, {
+  toJSON: function toJSON() {
+    return call(URL.prototype.toString, this);
+  }
+});