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/full/symbol/index.js

@@ -0,0 +1,15 @@
+'use strict';
+var parent = require('../../actual/symbol');
+require('../../modules/esnext.symbol.is-registered-symbol');
+require('../../modules/esnext.symbol.is-well-known-symbol');
+require('../../modules/esnext.symbol.custom-matcher');
+require('../../modules/esnext.symbol.observable');
+// TODO: Remove from `core-js@4`
+require('../../modules/esnext.symbol.is-registered');
+require('../../modules/esnext.symbol.is-well-known');
+require('../../modules/esnext.symbol.matcher');
+require('../../modules/esnext.symbol.metadata-key');
+require('../../modules/esnext.symbol.pattern-match');
+require('../../modules/esnext.symbol.replace-all');
+
+module.exports = parent;