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/promise/lib/finally.js

@@ -0,0 +1,16 @@
+'use strict';
+
+var Promise = require('./core.js');
+
+module.exports = Promise;
+Promise.prototype.finally = function (f) {
+  return this.then(function (value) {
+    return Promise.resolve(f()).then(function () {
+      return value;
+    });
+  }, function (err) {
+    return Promise.resolve(f()).then(function () {
+      throw err;
+    });
+  });
+};