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/@jest/core/build/TestWatcher.d.ts

@@ -0,0 +1,23 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+import emittery = require('emittery');
+declare type State = {
+    interrupted: boolean;
+};
+export default class TestWatcher extends emittery<{
+    change: State;
+}> {
+    state: State;
+    private _isWatchMode;
+    constructor({ isWatchMode }: {
+        isWatchMode: boolean;
+    });
+    setState(state: State): Promise<void>;
+    isInterrupted(): boolean;
+    isWatchMode(): boolean;
+}
+export {};