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/edit/cursorPosition.js

@@ -0,0 +1,35 @@
+"use strict";
+
+Object.defineProperty(exports, "__esModule", {
+  value: true
+});
+exports.isCursorAtEnd = isCursorAtEnd;
+exports.isCursorAtStart = isCursorAtStart;
+
+var _selectionRange = require("./selectionRange");
+
+var _getValue2 = require("./getValue");
+
+function isCursorAtEnd(element) {
+  var _getValue;
+
+  const {
+    selectionStart,
+    selectionEnd
+  } = (0, _selectionRange.getSelectionRange)(element);
+  return selectionStart === selectionEnd && (selectionStart != null ? selectionStart :
+  /* istanbul ignore next */
+  0) === ((_getValue = (0, _getValue2.getValue)(element)) != null ? _getValue :
+  /* istanbul ignore next */
+  '').length;
+}
+
+function isCursorAtStart(element) {
+  const {
+    selectionStart,
+    selectionEnd
+  } = (0, _selectionRange.getSelectionRange)(element);
+  return selectionStart === selectionEnd && (selectionStart != null ? selectionStart :
+  /* istanbul ignore next */
+  0) === 0;
+}