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/async-function/legacy.js

@@ -0,0 +1,18 @@
+'use strict';
+
+/** @type {import('.').AsyncFunctionConstructor | false} */
+var cached;
+
+/** @type {import('.')} */
+module.exports = function getAsyncFunction() {
+	if (typeof cached === 'undefined') {
+		try {
+			// eslint-disable-next-line no-new-func
+			cached = Function('return async function () {}')().constructor;
+		} catch (e) {
+			cached = false;
+		}
+	}
+	return cached;
+};
+