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.symbol.to-primitive.js

@@ -0,0 +1,11 @@
+'use strict';
+var defineWellKnownSymbol = require('../internals/well-known-symbol-define');
+var defineSymbolToPrimitive = require('../internals/symbol-define-to-primitive');
+
+// `Symbol.toPrimitive` well-known symbol
+// https://tc39.es/ecma262/#sec-symbol.toprimitive
+defineWellKnownSymbol('toPrimitive');
+
+// `Symbol.prototype[@@toPrimitive]` method
+// https://tc39.es/ecma262/#sec-symbol.prototype-@@toprimitive
+defineSymbolToPrimitive();