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/array-includes/polyfill.js

@@ -0,0 +1,13 @@
+'use strict';
+
+var implementation = require('./implementation');
+
+module.exports = function getPolyfill() {
+	if (
+		Array.prototype.includes
+		&& Array(1).includes(undefined) // https://bugzilla.mozilla.org/show_bug.cgi?id=1767541
+	) {
+		return Array.prototype.includes;
+	}
+	return implementation;
+};