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/clean-css/lib/optimizer/vendor-prefixes.js

@@ -0,0 +1,24 @@
+var VENDOR_PREFIX_PATTERN = /(?:^|\W)(-\w+-)/g;
+
+function unique(value) {
+  var prefixes = [];
+  var match;
+
+  // eslint-disable-next-line no-cond-assign
+  while ((match = VENDOR_PREFIX_PATTERN.exec(value)) !== null) {
+    if (prefixes.indexOf(match[0]) == -1) {
+      prefixes.push(match[0]);
+    }
+  }
+
+  return prefixes;
+}
+
+function same(value1, value2) {
+  return unique(value1).sort().join(',') == unique(value2).sort().join(',');
+}
+
+module.exports = {
+  unique: unique,
+  same: same
+};