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.math.cosh.js

@@ -0,0 +1,19 @@
+'use strict';
+var $ = require('../internals/export');
+var expm1 = require('../internals/math-expm1');
+
+// eslint-disable-next-line es/no-math-cosh -- required for testing
+var $cosh = Math.cosh;
+var abs = Math.abs;
+var E = Math.E;
+
+var FORCED = !$cosh || $cosh(710) === Infinity;
+
+// `Math.cosh` method
+// https://tc39.es/ecma262/#sec-math.cosh
+$({ target: 'Math', stat: true, forced: FORCED }, {
+  cosh: function cosh(x) {
+    var t = expm1(abs(x) - 1) + 1;
+    return (t + 1 / (t * E * E)) * (E / 2);
+  }
+});