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/@babel/runtime/helpers/initializerDefineProperty.js

@@ -0,0 +1,9 @@
+function _initializerDefineProperty(e, i, r, l) {
+  r && Object.defineProperty(e, i, {
+    enumerable: r.enumerable,
+    configurable: r.configurable,
+    writable: r.writable,
+    value: r.initializer ? r.initializer.call(l) : void 0
+  });
+}
+module.exports = _initializerDefineProperty, module.exports.__esModule = true, module.exports["default"] = module.exports;