feat: Implement in-app service worker update notification

Co-authored-by: aider (gemini/gemini-2.5-pro) <aider@aider.chat>

webclient/src/index.js

@@ -8,4 +8,8 @@ ReactDOM.render(<App />, document.getElementById('root'));
 // If you want your app to work offline and load faster, you can change
 // // unregister() to register() below. Note this comes with some pitfalls.
 // // Learn more about service workers: https://bit.ly/CRA-PWA
-serviceWorker.unregister();
+serviceWorker.register({
+  onUpdate: registration => {
+    window.dispatchEvent(new CustomEvent('swUpdate', { detail: registration }));
+  }
+});