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/helpers/IsArray.js

@@ -0,0 +1,12 @@
+'use strict';
+
+var GetIntrinsic = require('get-intrinsic');
+
+var $Array = GetIntrinsic('%Array%');
+
+// eslint-disable-next-line global-require
+var toStr = !$Array.isArray && require('call-bound')('Object.prototype.toString');
+
+module.exports = $Array.isArray || function IsArray(argument) {
+	return toStr(argument) === '[object Array]';
+};