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/es/json/stringify.js

@@ -0,0 +1,13 @@
+'use strict';
+require('../../modules/es.date.to-json');
+require('../../modules/es.json.stringify');
+var path = require('../../internals/path');
+var apply = require('../../internals/function-apply');
+
+// eslint-disable-next-line es/no-json -- safe
+if (!path.JSON) path.JSON = { stringify: JSON.stringify };
+
+// eslint-disable-next-line no-unused-vars -- required for `.length`
+module.exports = function stringify(it, replacer, space) {
+  return apply(path.JSON.stringify, null, arguments);
+};