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/array-buffer-is-detached.js

@@ -0,0 +1,17 @@
+'use strict';
+var globalThis = require('../internals/global-this');
+var NATIVE_ARRAY_BUFFER = require('../internals/array-buffer-basic-detection');
+var arrayBufferByteLength = require('../internals/array-buffer-byte-length');
+
+var DataView = globalThis.DataView;
+
+module.exports = function (O) {
+  if (!NATIVE_ARRAY_BUFFER || arrayBufferByteLength(O) !== 0) return false;
+  try {
+    // eslint-disable-next-line no-new -- thrower
+    new DataView(O);
+    return false;
+  } catch (error) {
+    return true;
+  }
+};