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/array-method-is-strict.js

@@ -0,0 +1,10 @@
+'use strict';
+var fails = require('../internals/fails');
+
+module.exports = function (METHOD_NAME, argument) {
+  var method = [][METHOD_NAME];
+  return !!method && fails(function () {
+    // eslint-disable-next-line no-useless-call -- required for testing
+    method.call(null, argument || function () { return 1; }, 1);
+  });
+};