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/errors.js

@@ -0,0 +1,14 @@
+/**
+ * unopinionated config. just the things that are necessarily runtime errors
+ * waiting to happen.
+ * @type {Object}
+ */
+module.exports = {
+  plugins: ['import'],
+  rules: { 'import/no-unresolved': 2,
+    'import/named': 2,
+    'import/namespace': 2,
+    'import/default': 2,
+    'import/export': 2,
+  },
+};