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/modules/esnext.symbol.is-well-known.js

@@ -0,0 +1,10 @@
+'use strict';
+var $ = require('../internals/export');
+var isWellKnownSymbol = require('../internals/symbol-is-well-known');
+
+// `Symbol.isWellKnown` method
+// obsolete version of https://tc39.es/proposal-symbol-predicates/#sec-symbol-iswellknownsymbol
+// We should patch it for newly added well-known symbols. If it's not required, this module just will not be injected
+$({ target: 'Symbol', stat: true, name: 'isWellKnownSymbol', forced: true }, {
+  isWellKnown: isWellKnownSymbol
+});