pwa / offline mode

- @vite-pwa/sveltekit: workbox precache (incl. pdfjs worker), generated manifest, prompt-style updates via PwaUpdatePrompt toast
- prerendered routes for offline navigation, PWA icons, theme-color + apple-touch-icon
- pwa offline/update e2e suite (pnpm test:pwa, playwright.pwa.config.ts)
- datenschutz: offline/install section; prettier cleanup of shadcn components

src/routes/+layout.svelte

@@ -1,12 +1,18 @@
 <script lang="ts">
 	import './layout.css';
+	import { pwaInfo } from 'virtual:pwa-info';
 	import favicon from '$lib/assets/favicon.svg';
+	import PwaUpdatePrompt from '$lib/components/PwaUpdatePrompt.svelte';
 
 	let { children } = $props();
 </script>
 
 <svelte:head>
 	<link rel="icon" href={favicon} />
+	{#if pwaInfo}
+		<!-- rendered on the client only: the manifest is part of the production build output -->
+		{@html pwaInfo.webManifest.linkTag}
+	{/if}
 </svelte:head>
 <div class="flex min-h-dvh flex-col">
 	<header style="height:72px" class="grid shrink-0 place-content-center bg-white shadow">
@@ -19,6 +25,8 @@
 		{@render children()}
 	</div>
 
+	<PwaUpdatePrompt />
+
 	<footer
 		class="mt-8.75 flex h-96 min-h-78.5 shrink-0 flex-col justify-end gap-15 px-4 py-8.75 text-white"
 		style="background-image: url('/footer.svg');background-position: top right; background-size: cover; background-repeat: no-repeat"