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/to-index.js

@@ -0,0 +1,15 @@
+'use strict';
+var toIntegerOrInfinity = require('../internals/to-integer-or-infinity');
+var toLength = require('../internals/to-length');
+
+var $RangeError = RangeError;
+
+// `ToIndex` abstract operation
+// https://tc39.es/ecma262/#sec-toindex
+module.exports = function (it) {
+  if (it === undefined) return 0;
+  var number = toIntegerOrInfinity(it);
+  var length = toLength(number);
+  if (number !== length) throw new $RangeError('Wrong length or index');
+  return length;
+};