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/autoprefixer/lib/hacks/flex-spec.js

@@ -0,0 +1,19 @@
+/**
+ * Return flexbox spec versions by prefix
+ */
+module.exports = function (prefix) {
+  let spec
+  if (prefix === '-webkit- 2009' || prefix === '-moz-') {
+    spec = 2009
+  } else if (prefix === '-ms-') {
+    spec = 2012
+  } else if (prefix === '-webkit-') {
+    spec = 'final'
+  }
+
+  if (prefix === '-webkit- 2009') {
+    prefix = '-webkit-'
+  }
+
+  return [spec, prefix]
+}