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/@testing-library/user-event/dist/utils/focus/getActiveElement.js

@@ -0,0 +1,26 @@
+"use strict";
+
+Object.defineProperty(exports, "__esModule", {
+  value: true
+});
+exports.getActiveElement = getActiveElement;
+
+var _isDisabled = require("../misc/isDisabled");
+
+function getActiveElement(document) {
+  const activeElement = document.activeElement;
+
+  if (activeElement != null && activeElement.shadowRoot) {
+    return getActiveElement(activeElement.shadowRoot);
+  } else {
+    // Browser does not yield disabled elements as document.activeElement - jsdom does
+    if ((0, _isDisabled.isDisabled)(activeElement)) {
+      return document.ownerDocument ? // TODO: verify behavior in ShadowRoot
+
+      /* istanbul ignore next */
+      document.ownerDocument.body : document.body;
+    }
+
+    return activeElement;
+  }
+}