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/internals/object-keys.js

@@ -0,0 +1,10 @@
+'use strict';
+var internalObjectKeys = require('../internals/object-keys-internal');
+var enumBugKeys = require('../internals/enum-bug-keys');
+
+// `Object.keys` method
+// https://tc39.es/ecma262/#sec-object.keys
+// eslint-disable-next-line es/no-object-keys -- safe
+module.exports = Object.keys || function keys(O) {
+  return internalObjectKeys(O, enumBugKeys);
+};