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/modules/web.set-interval.js

@@ -0,0 +1,12 @@
+'use strict';
+var $ = require('../internals/export');
+var globalThis = require('../internals/global-this');
+var schedulersFix = require('../internals/schedulers-fix');
+
+var setInterval = schedulersFix(globalThis.setInterval, true);
+
+// Bun / IE9- setInterval additional parameters fix
+// https://html.spec.whatwg.org/multipage/timers-and-user-prompts.html#dom-setinterval
+$({ global: true, bind: true, forced: globalThis.setInterval !== setInterval }, {
+  setInterval: setInterval
+});