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-environment-node/build/index.d.ts

@@ -0,0 +1,29 @@
+/**
+ * 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.
+ */
+/// <reference types="node" />
+import { Context } from 'vm';
+import type { JestEnvironment } from '@jest/environment';
+import { LegacyFakeTimers, ModernFakeTimers } from '@jest/fake-timers';
+import type { Config, Global } from '@jest/types';
+import { ModuleMocker } from 'jest-mock';
+declare type Timer = {
+    id: number;
+    ref: () => Timer;
+    unref: () => Timer;
+};
+declare class NodeEnvironment implements JestEnvironment<Timer> {
+    context: Context | null;
+    fakeTimers: LegacyFakeTimers<Timer> | null;
+    fakeTimersModern: ModernFakeTimers | null;
+    global: Global.Global;
+    moduleMocker: ModuleMocker | null;
+    constructor(config: Config.ProjectConfig);
+    setup(): Promise<void>;
+    teardown(): Promise<void>;
+    getVmContext(): Context | null;
+}
+export = NodeEnvironment;