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/modules/es.string.includes.js

@@ -0,0 +1,21 @@
+'use strict';
+var $ = require('../internals/export');
+var uncurryThis = require('../internals/function-uncurry-this');
+var notARegExp = require('../internals/not-a-regexp');
+var requireObjectCoercible = require('../internals/require-object-coercible');
+var toString = require('../internals/to-string');
+var correctIsRegExpLogic = require('../internals/correct-is-regexp-logic');
+
+var stringIndexOf = uncurryThis(''.indexOf);
+
+// `String.prototype.includes` method
+// https://tc39.es/ecma262/#sec-string.prototype.includes
+$({ target: 'String', proto: true, forced: !correctIsRegExpLogic('includes') }, {
+  includes: function includes(searchString /* , position = 0 */) {
+    return !!~stringIndexOf(
+      toString(requireObjectCoercible(this)),
+      toString(notARegExp(searchString)),
+      arguments.length > 1 ? arguments[1] : undefined
+    );
+  }
+});