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/eslint-plugin-import/config/react-native.js

@@ -0,0 +1,13 @@
+/**
+ * - adds platform extensions to Node resolver
+ */
+module.exports = {
+  settings: {
+    'import/resolver': {
+      node: {
+        // Note: will not complain if only _one_ of these files exists.
+        extensions: ['.js', '.web.js', '.ios.js', '.android.js'],
+      },
+    },
+  },
+};