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/internals/species-constructor.js

@@ -0,0 +1,15 @@
+'use strict';
+var anObject = require('../internals/an-object');
+var aConstructor = require('../internals/a-constructor');
+var isNullOrUndefined = require('../internals/is-null-or-undefined');
+var wellKnownSymbol = require('../internals/well-known-symbol');
+
+var SPECIES = wellKnownSymbol('species');
+
+// `SpeciesConstructor` abstract operation
+// https://tc39.es/ecma262/#sec-speciesconstructor
+module.exports = function (O, defaultConstructor) {
+  var C = anObject(O).constructor;
+  var S;
+  return C === undefined || isNullOrUndefined(S = anObject(C)[SPECIES]) ? defaultConstructor : aConstructor(S);
+};