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/es-to-primitive/index.d.ts

@@ -0,0 +1,11 @@
+import ES5 from './es5';
+import ES6 from './es6';
+import ES2015 from './es2015';
+
+declare const ToPrimitive: typeof ES2015 & {
+    readonly ES5: typeof ES5;
+    /** @deprecated */
+    readonly ES6: typeof ES6;
+    readonly ES2015: typeof ES2015;
+};
+export = ToPrimitive;