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/dom-accessibility-api/dist/polyfills/SetLike.d.ts

@@ -0,0 +1,14 @@
+declare global {
+    class Set<T> {
+        constructor(items?: T[]);
+        add(value: T): this;
+        clear(): void;
+        delete(value: T): boolean;
+        forEach(callbackfn: (value: T, value2: T, set: Set<T>) => void, thisArg?: unknown): void;
+        has(value: T): boolean;
+        readonly size: number;
+    }
+}
+declare const _default: typeof Set;
+export default _default;
+//# sourceMappingURL=SetLike.d.ts.map