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/modules/es.array-buffer.detached.js

@@ -0,0 +1,17 @@
+'use strict';
+var DESCRIPTORS = require('../internals/descriptors');
+var defineBuiltInAccessor = require('../internals/define-built-in-accessor');
+var isDetached = require('../internals/array-buffer-is-detached');
+
+var ArrayBufferPrototype = ArrayBuffer.prototype;
+
+// `ArrayBuffer.prototype.detached` getter
+// https://tc39.es/ecma262/#sec-get-arraybuffer.prototype.detached
+if (DESCRIPTORS && !('detached' in ArrayBufferPrototype)) {
+  defineBuiltInAccessor(ArrayBufferPrototype, 'detached', {
+    configurable: true,
+    get: function detached() {
+      return isDetached(this);
+    }
+  });
+}