fix(ui): register the service worker in production only

SvelteKit's automatic SW registration also runs under `vite dev`, where
the worker intercepted/cached the dev-server e2e suite (42 failures).
Disable auto-registration (kit.serviceWorker.register: false) and
register the worker manually from the root layout guarded by `!dev`, so
`vite dev` and the e2e suite run worker-free while the production build —
and the PWA preview test — still install it.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

ui/frontend/src/routes/+layout.svelte

@@ -4,6 +4,7 @@
 	import { onMount } from "svelte";
 	import { goto } from "$app/navigation";
 	import { page } from "$app/state";
+	import { dev } from "$app/environment";
 	import { i18n } from "$lib/i18n/index.svelte";
 	import { session } from "$lib/session-store.svelte";
 	import { eventStream } from "../api/events.svelte";
@@ -21,6 +22,12 @@
 
 	onMount(() => {
 		void session.init();
+		// Production-only service-worker registration (auto-register is off
+		// in svelte.config.js) so `vite dev` and the dev-server e2e suite
+		// run without the worker intercepting requests.
+		if (!dev && "serviceWorker" in navigator) {
+			void navigator.serviceWorker.register("/service-worker.js");
+		}
 		return () => {
 			eventStream.stop();
 			streamSessionId = null;