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/internals/set-difference.js

@@ -0,0 +1,26 @@
+'use strict';
+var aSet = require('../internals/a-set');
+var SetHelpers = require('../internals/set-helpers');
+var clone = require('../internals/set-clone');
+var size = require('../internals/set-size');
+var getSetRecord = require('../internals/get-set-record');
+var iterateSet = require('../internals/set-iterate');
+var iterateSimple = require('../internals/iterate-simple');
+
+var has = SetHelpers.has;
+var remove = SetHelpers.remove;
+
+// `Set.prototype.difference` method
+// https://tc39.es/ecma262/#sec-set.prototype.difference
+module.exports = function difference(other) {
+  var O = aSet(this);
+  var otherRec = getSetRecord(other);
+  var result = clone(O);
+  if (size(O) <= otherRec.size) iterateSet(O, function (e) {
+    if (otherRec.includes(e)) remove(result, e);
+  });
+  else iterateSimple(otherRec.getIterator(), function (e) {
+    if (has(result, e)) remove(result, e);
+  });
+  return result;
+};