fix: register PWA service worker via virtual:pwa-register for offline support

@vite-pwa/sveltekit does not auto-inject SW registration into SSR HTML.
Add explicit registration via virtual:pwa-register in root layout onMount,
inject webmanifest link via virtual:pwa-info, disable SvelteKit's built-in
SW registration to avoid conflicts, and add required dependencies.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/app.d.ts

@@ -1,3 +1,6 @@
+/// <reference types="vite-plugin-pwa/info" />
+/// <reference types="vite-plugin-pwa/vanillajs" />
+
 // See https://svelte.dev/docs/kit/types#app.d.ts
 // for information about these interfaces
 declare global {

src/routes/+layout.svelte

@@ -1,7 +1,30 @@
 <script lang="ts">
 	import '../app.css';
+	import { onMount } from 'svelte';
+	import { pwaInfo } from 'virtual:pwa-info';
 
 	let { children } = $props();
+
+	onMount(async () => {
+		if (pwaInfo) {
+			const { registerSW } = await import('virtual:pwa-register');
+			registerSW({
+				immediate: true,
+				onRegistered(r: ServiceWorkerRegistration | undefined) {
+					console.log('SW Registered:', r);
+				},
+				onRegisterError(error: Error) {
+					console.log('SW registration error', error);
+				}
+			});
+		}
+	});
+
+	const webManifest = $derived(pwaInfo ? pwaInfo.webManifest.linkTag : '');
 </script>
 
+<svelte:head>
+	{@html webManifest}
+</svelte:head>
+
 {@render children()}