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/toSetter.js

@@ -0,0 +1,10 @@
+function _toSetter(t, e, n) {
+  e || (e = []);
+  var r = e.length++;
+  return Object.defineProperty({}, "_", {
+    set: function set(o) {
+      e[r] = o, t.apply(n, e);
+    }
+  });
+}
+module.exports = _toSetter, module.exports.__esModule = true, module.exports["default"] = module.exports;