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/http-proxy-middleware/dist/index.d.ts

@@ -0,0 +1,4 @@
+import { Filter, Options } from './types';
+export declare function createProxyMiddleware(context: Filter | Options, options?: Options): import("./types").RequestHandler;
+export * from './handlers';
+export { Filter, Options, RequestHandler } from './types';