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/is-weakref/index.js

@@ -0,0 +1,24 @@
+'use strict';
+
+var callBound = require('call-bound');
+
+// eslint-disable-next-line no-extra-parens
+var $deref = /** @type {<T extends WeakKey>(thisArg: WeakRef<T>) => T | undefined} */ (callBound('WeakRef.prototype.deref', true));
+
+/** @type {import('.')} */
+module.exports = typeof WeakRef === 'undefined'
+	? function isWeakRef(_value) { // eslint-disable-line no-unused-vars
+		return false;
+	}
+	: function isWeakRef(value) {
+		if (!value || typeof value !== 'object') {
+			return false;
+		}
+		try {
+			// @ts-expect-error
+			$deref(value);
+			return true;
+		} catch (e) {
+			return false;
+		}
+	};