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/regexp-unsupported-ncg.js

@@ -0,0 +1,12 @@
+'use strict';
+var fails = require('../internals/fails');
+var globalThis = require('../internals/global-this');
+
+// babel-minify and Closure Compiler transpiles RegExp('(?<a>b)', 'g') -> /(?<a>b)/g and it causes SyntaxError
+var $RegExp = globalThis.RegExp;
+
+module.exports = fails(function () {
+  var re = $RegExp('(?<a>b)', 'g');
+  return re.exec('b').groups.a !== 'b' ||
+    'b'.replace(re, '$<a>c') !== 'bc';
+});