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/modules/esnext.iterator.windows.js

@@ -0,0 +1,11 @@
+'use strict';
+var $ = require('../internals/export');
+var iteratorWindow = require('../internals/iterator-window');
+
+// `Iterator.prototype.windows` method
+// https://github.com/tc39/proposal-iterator-chunking
+$({ target: 'Iterator', proto: true, real: true, forced: true }, {
+  windows: function windows(windowSize) {
+    return iteratorWindow(this, windowSize, false);
+  }
+});