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/to-integer-or-infinity.js

@@ -0,0 +1,10 @@
+'use strict';
+var trunc = require('../internals/math-trunc');
+
+// `ToIntegerOrInfinity` abstract operation
+// https://tc39.es/ecma262/#sec-tointegerorinfinity
+module.exports = function (argument) {
+  var number = +argument;
+  // eslint-disable-next-line no-self-compare -- NaN check
+  return number !== number || number === 0 ? 0 : trunc(number);
+};