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/signal-exit/dist/cjs/browser.d.ts

@@ -0,0 +1,12 @@
+/**
+ * This is a browser shim that provides the same functional interface
+ * as the main node export, but it does nothing.
+ * @module
+ */
+import type { Handler } from './index.js';
+export declare const onExit: (cb: Handler, opts: {
+    alwaysLast?: boolean;
+}) => () => void;
+export declare const load: () => void;
+export declare const unload: () => void;
+//# sourceMappingURL=browser.d.ts.map