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/pairs.js

@@ -0,0 +1,15 @@
+var keys = require('./keys.js');
+
+// Convert an object into a list of `[key, value]` pairs.
+// The opposite of `_.object` with one argument.
+function pairs(obj) {
+  var _keys = keys(obj);
+  var length = _keys.length;
+  var pairs = Array(length);
+  for (var i = 0; i < length; i++) {
+    pairs[i] = [_keys[i], obj[_keys[i]]];
+  }
+  return pairs;
+}
+
+module.exports = pairs;