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/set-union.js

@@ -0,0 +1,18 @@
+'use strict';
+var aSet = require('../internals/a-set');
+var add = require('../internals/set-helpers').add;
+var clone = require('../internals/set-clone');
+var getSetRecord = require('../internals/get-set-record');
+var iterateSimple = require('../internals/iterate-simple');
+
+// `Set.prototype.union` method
+// https://tc39.es/ecma262/#sec-set.prototype.union
+module.exports = function union(other) {
+  var O = aSet(this);
+  var keysIter = getSetRecord(other).getIterator();
+  var result = clone(O);
+  iterateSimple(keysIter, function (it) {
+    add(result, it);
+  });
+  return result;
+};