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/core-js-pure/proposals/async-explicit-resource-management.js

@@ -0,0 +1,7 @@
+'use strict';
+// TODO: Remove from `core-js@4`
+// https://github.com/tc39/proposal-async-explicit-resource-management
+require('../modules/esnext.suppressed-error.constructor');
+require('../modules/esnext.async-disposable-stack.constructor');
+require('../modules/esnext.async-iterator.async-dispose');
+require('../modules/esnext.symbol.async-dispose');