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/@pmmmwh/react-refresh-webpack-plugin/lib/globals.js

@@ -0,0 +1,22 @@
+/**
+ * Gets current bundle's global scope identifier for React Refresh.
+ * @param {Record<string, string>} runtimeGlobals The Webpack runtime globals.
+ * @returns {string} The React Refresh global scope within the Webpack bundle.
+ */
+module.exports.getRefreshGlobalScope = (runtimeGlobals) => {
+  return `${runtimeGlobals.require || '__webpack_require__'}.$Refresh$`;
+};
+
+/**
+ * Gets current Webpack version according to features on the compiler instance.
+ * @param {import('webpack').Compiler} compiler The current Webpack compiler instance.
+ * @returns {number} The current Webpack version.
+ */
+module.exports.getWebpackVersion = (compiler) => {
+  if (!compiler.hooks) {
+    throw new Error(`[ReactRefreshPlugin] Webpack version is not supported!`);
+  }
+
+  // Webpack v5+ implements compiler caching
+  return 'cache' in compiler ? 5 : 4;
+};