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/an-uint8-array.js

@@ -0,0 +1,11 @@
+'use strict';
+var classof = require('../internals/classof');
+
+var $TypeError = TypeError;
+
+// Perform ? RequireInternalSlot(argument, [[TypedArrayName]])
+// If argument.[[TypedArrayName]] is not "Uint8Array", throw a TypeError exception
+module.exports = function (argument) {
+  if (classof(argument) === 'Uint8Array') return argument;
+  throw new $TypeError('Argument is not an Uint8Array');
+};