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-module-utils/visit.d.ts

@@ -0,0 +1,9 @@
+import type { Node } from 'estree';
+
+declare function visit(
+    node: Node,
+    keys: { [k in Node['type']]?: (keyof Node)[] },
+    visitorSpec: { [k in Node['type'] | `${Node['type']}:Exit`]?: Function }
+): void;
+
+export default visit;