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/callsites/index.js

@@ -0,0 +1,13 @@
+'use strict';
+
+const callsites = () => {
+	const _prepareStackTrace = Error.prepareStackTrace;
+	Error.prepareStackTrace = (_, stack) => stack;
+	const stack = new Error().stack.slice(1);
+	Error.prepareStackTrace = _prepareStackTrace;
+	return stack;
+};
+
+module.exports = callsites;
+// TODO: Remove this for the next major release
+module.exports.default = callsites;