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/shared-store.js

@@ -0,0 +1,15 @@
+'use strict';
+var IS_PURE = require('../internals/is-pure');
+var globalThis = require('../internals/global-this');
+var defineGlobalProperty = require('../internals/define-global-property');
+
+var SHARED = '__core-js_shared__';
+var store = module.exports = globalThis[SHARED] || defineGlobalProperty(SHARED, {});
+
+(store.versions || (store.versions = [])).push({
+  version: '3.44.0',
+  mode: IS_PURE ? 'pure' : 'global',
+  copyright: '© 2014-2025 Denis Pushkarev (zloirock.ru)',
+  license: 'https://github.com/zloirock/core-js/blob/v3.44.0/LICENSE',
+  source: 'https://github.com/zloirock/core-js'
+});