refactor(pwa): replace custom service workers with Vite PWA plugin and centralize offline page

Remove hand-written sw.js, offline.html, and manifest.json from todo/skilltree/zitare web apps
in favor of the Workbox-based service worker generated by @vite-pwa/sveltekit. This fixes an
issue where the custom SW could get stuck serving the offline fallback page even when the server
was reachable. Also extracts the duplicated offline page (~80 lines each across 19 apps) into a
shared OfflinePage component in @manacore/shared-ui with 3 props (appName, offlineMessage,
accentColor), reducing each app's offline route to an 8-line wrapper.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/shared-ui/src/index.ts

@@ -155,6 +155,7 @@ export type { QuickInputItem, QuickAction, CreatePreview, InputBarSettings } fro
 
 // Pages
 export { default as AppsPage } from './pages/AppsPage.svelte';
+export { default as OfflinePage } from './pages/OfflinePage.svelte';
 
 // Charts - Statistics Visualization
 export {

packages/shared-ui/src/pages/OfflinePage.svelte

@@ -0,0 +1,119 @@
+<script lang="ts">
+	import { onMount } from 'svelte';
+
+	interface Props {
+		appName: string;
+		offlineMessage: string;
+		accentColor?: string;
+	}
+
+	let { appName, offlineMessage, accentColor = '#3b82f6' }: Props = $props();
+
+	let isOnline = $state(false);
+
+	onMount(() => {
+		isOnline = navigator.onLine;
+
+		const handleOnline = () => {
+			isOnline = true;
+			setTimeout(() => {
+				window.location.href = '/';
+			}, 1000);
+		};
+
+		const handleOffline = () => {
+			isOnline = false;
+		};
+
+		window.addEventListener('online', handleOnline);
+		window.addEventListener('offline', handleOffline);
+
+		return () => {
+			window.removeEventListener('online', handleOnline);
+			window.removeEventListener('offline', handleOffline);
+		};
+	});
+</script>
+
+<svelte:head>
+	<title>Offline - {appName}</title>
+</svelte:head>
+
+<div class="min-h-screen bg-slate-900 flex items-center justify-center px-4">
+	<div class="text-center max-w-md">
+		<div class="mb-8">
+			<svg
+				class="w-24 h-24 mx-auto text-slate-500"
+				fill="none"
+				stroke="currentColor"
+				viewBox="0 0 24 24"
+			>
+				<path
+					stroke-linecap="round"
+					stroke-linejoin="round"
+					stroke-width="1.5"
+					d="M18.364 5.636a9 9 0 010 12.728m0 0l-2.829-2.829m2.829 2.829L21 21M15.536 8.464a5 5 0 010 7.072m0 0l-2.829-2.829m-4.243 2.829a5 5 0 01-.354-7.072L8.95 7.636m1.414 5.657L7.535 16.12m8.485 0a5 5 0 01-7.07 0"
+				/>
+				<path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M3 3l18 18" />
+			</svg>
+		</div>
+
+		<h1 class="text-2xl font-bold text-white mb-4">
+			{isOnline ? 'Verbindung wiederhergestellt!' : 'Du bist offline'}
+		</h1>
+
+		<p class="text-slate-400 mb-8">
+			{#if isOnline}
+				Du wirst gleich weitergeleitet...
+			{:else}
+				{offlineMessage}
+			{/if}
+		</p>
+
+		{#if !isOnline}
+			<div class="space-y-4">
+				<a
+					href="/"
+					class="inline-flex items-center justify-center px-6 py-3 text-white font-medium rounded-lg transition-colors"
+					style="background-color: {accentColor};"
+					onmouseenter={(e) => {
+						e.currentTarget.style.filter = 'brightness(0.85)';
+					}}
+					onmouseleave={(e) => {
+						e.currentTarget.style.filter = '';
+					}}
+				>
+					<svg class="w-5 h-5 mr-2" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+						<path
+							stroke-linecap="round"
+							stroke-linejoin="round"
+							stroke-width="2"
+							d="M3 12l2-2m0 0l7-7 7 7M5 10v10a1 1 0 001 1h3m10-11l2 2m-2-2v10a1 1 0 01-1 1h-3m-6 0a1 1 0 001-1v-4a1 1 0 011-1h2a1 1 0 011 1v4a1 1 0 001 1m-6 0h6"
+						/>
+					</svg>
+					Zur Startseite
+				</a>
+
+				<button
+					onclick={() => window.location.reload()}
+					class="block w-full px-6 py-3 text-slate-400 hover:text-white transition-colors"
+				>
+					Erneut versuchen
+				</button>
+			</div>
+		{:else}
+			<div class="flex items-center justify-center text-green-400">
+				<svg class="w-5 h-5 mr-2 animate-spin" fill="none" viewBox="0 0 24 24">
+					<circle class="opacity-25" cx="12" cy="12" r="10" stroke="currentColor" stroke-width="4"
+					></circle>
+					<path
+						class="opacity-75"
+						fill="currentColor"
+						d="M4 12a8 8 0 018-8V0C5.373 0 0 5.373 0 12h4zm2 5.291A7.962 7.962 0 014 12H0c0 3.042 1.135 5.824 3 7.938l3-2.647z"
+					></path>
+				</svg>
+				Weiterleitung...
+			</div>
+		{/if}
+	</div>
+</div>