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/underscore/cjs/contains.js

@@ -0,0 +1,12 @@
+var _isArrayLike = require('./_isArrayLike.js');
+var values = require('./values.js');
+var indexOf = require('./indexOf.js');
+
+// Determine if the array or object contains a given item (using `===`).
+function contains(obj, item, fromIndex, guard) {
+  if (!_isArrayLike(obj)) obj = values(obj);
+  if (typeof fromIndex != 'number' || guard) fromIndex = 0;
+  return indexOf(obj, item, fromIndex) >= 0;
+}
+
+module.exports = contains;