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/readable-stream/experimentalWarning.js

@@ -0,0 +1,17 @@
+'use strict'
+
+var experimentalWarnings = new Set();
+
+function emitExperimentalWarning(feature) {
+  if (experimentalWarnings.has(feature)) return;
+  var msg = feature + ' is an experimental feature. This feature could ' +
+       'change at any time';
+  experimentalWarnings.add(feature);
+  process.emitWarning(msg, 'ExperimentalWarning');
+}
+
+function noop() {}
+
+module.exports.emitExperimentalWarning = process.emitWarning
+  ? emitExperimentalWarning
+  : noop;