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/full/set/symmetric-difference.js

@@ -0,0 +1,9 @@
+'use strict';
+require('../../actual/set/symmetric-difference');
+require('../../modules/es.array.iterator');
+require('../../modules/es.string.iterator');
+require('../../modules/esnext.set.symmetric-difference');
+require('../../modules/web.dom-collections.iterator');
+var entryUnbind = require('../../internals/entry-unbind');
+
+module.exports = entryUnbind('Set', 'symmetricDifference');