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/internals/object-get-own-property-names.js

@@ -0,0 +1,12 @@
+'use strict';
+var internalObjectKeys = require('../internals/object-keys-internal');
+var enumBugKeys = require('../internals/enum-bug-keys');
+
+var hiddenKeys = enumBugKeys.concat('length', 'prototype');
+
+// `Object.getOwnPropertyNames` method
+// https://tc39.es/ecma262/#sec-object.getownpropertynames
+// eslint-disable-next-line es/no-object-getownpropertynames -- safe
+exports.f = Object.getOwnPropertyNames || function getOwnPropertyNames(O) {
+  return internalObjectKeys(O, hiddenKeys);
+};