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/react-dev-utils/ignoredFiles.js

@@ -0,0 +1,20 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+'use strict';
+
+const path = require('path');
+const escape = require('escape-string-regexp');
+
+module.exports = function ignoredFiles(appSrc) {
+  return new RegExp(
+    `^(?!${escape(
+      path.normalize(appSrc + '/').replace(/[\\]+/g, '/')
+    )}).+/node_modules/`,
+    'g'
+  );
+};