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/redirectServedPathMiddleware.js

@@ -0,0 +1,26 @@
+/**
+ * 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');
+
+module.exports = function createRedirectServedPathMiddleware(servedPath) {
+  // remove end slash so user can land on `/test` instead of `/test/`
+  servedPath = servedPath.slice(0, -1);
+  return function redirectServedPathMiddleware(req, res, next) {
+    if (
+      servedPath === '' ||
+      req.url === servedPath ||
+      req.url.startsWith(servedPath)
+    ) {
+      next();
+    } else {
+      const newPath = path.posix.join(servedPath, req.path !== '/' ? req.path : '');
+      res.redirect(newPath);
+    }
+  };
+};