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/proposals/reflect-metadata.js

@@ -0,0 +1,11 @@
+'use strict';
+// https://github.com/rbuckton/reflect-metadata
+require('../modules/esnext.reflect.define-metadata');
+require('../modules/esnext.reflect.delete-metadata');
+require('../modules/esnext.reflect.get-metadata');
+require('../modules/esnext.reflect.get-metadata-keys');
+require('../modules/esnext.reflect.get-own-metadata');
+require('../modules/esnext.reflect.get-own-metadata-keys');
+require('../modules/esnext.reflect.has-metadata');
+require('../modules/esnext.reflect.has-own-metadata');
+require('../modules/esnext.reflect.metadata');