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/5/abs.js

@@ -0,0 +1,9 @@
+'use strict';
+
+var $abs = require('math-intrinsics/abs');
+
+// https://262.ecma-international.org/5.1/#sec-5.2
+
+module.exports = function abs(x) {
+	return $abs(x);
+};