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/modules/es.string.trim-end.js

@@ -0,0 +1,12 @@
+'use strict';
+// TODO: Remove this line from `core-js@4`
+require('../modules/es.string.trim-right');
+var $ = require('../internals/export');
+var trimEnd = require('../internals/string-trim-end');
+
+// `String.prototype.trimEnd` method
+// https://tc39.es/ecma262/#sec-string.prototype.trimend
+// eslint-disable-next-line es/no-string-prototype-trimstart-trimend -- safe
+$({ target: 'String', proto: true, name: 'trimEnd', forced: ''.trimEnd !== trimEnd }, {
+  trimEnd: trimEnd
+});