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-pure/internals/structured-clone-proper-transfer.js

@@ -0,0 +1,16 @@
+'use strict';
+var globalThis = require('../internals/global-this');
+var fails = require('../internals/fails');
+var V8 = require('../internals/environment-v8-version');
+var ENVIRONMENT = require('../internals/environment');
+
+var structuredClone = globalThis.structuredClone;
+
+module.exports = !!structuredClone && !fails(function () {
+  // prevent V8 ArrayBufferDetaching protector cell invalidation and performance degradation
+  // https://github.com/zloirock/core-js/issues/679
+  if ((ENVIRONMENT === 'DENO' && V8 > 92) || (ENVIRONMENT === 'NODE' && V8 > 94) || (ENVIRONMENT === 'BROWSER' && V8 > 97)) return false;
+  var buffer = new ArrayBuffer(8);
+  var clone = structuredClone(buffer, { transfer: [buffer] });
+  return buffer.byteLength !== 0 || clone.byteLength !== 8;
+});