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/es-abstract/2015/ToPropertyKey.js

@@ -0,0 +1,15 @@
+'use strict';
+
+var GetIntrinsic = require('get-intrinsic');
+
+var $String = GetIntrinsic('%String%');
+
+var ToPrimitive = require('./ToPrimitive');
+var ToString = require('./ToString');
+
+// https://262.ecma-international.org/6.0/#sec-topropertykey
+
+module.exports = function ToPropertyKey(argument) {
+	var key = ToPrimitive(argument, $String);
+	return typeof key === 'symbol' ? key : ToString(key);
+};