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/istanbul-lib-coverage/lib/data-properties.js

@@ -0,0 +1,12 @@
+'use strict';
+
+module.exports = function dataProperties(klass, properties) {
+    properties.forEach(p => {
+        Object.defineProperty(klass.prototype, p, {
+            enumerable: true,
+            get() {
+                return this.data[p];
+            }
+        });
+    });
+};