feat(webapp): add offline shell and iPhone install guidance

WebApp/src/routes/+layout.svelte

@@ -5,7 +5,14 @@
 	import { registerSW } from 'virtual:pwa-register';
 	import favicon from '$lib/assets/favicon.svg';
 	import { appController } from '$lib/app/controller';
-	import { clearInstallPrompt, setInstallPrompt, setOfflineReady, setUpdateAvailable } from '$lib/pwa';
+	import {
+		clearInstallPrompt,
+		setInstallPrompt,
+		setOfflineReady,
+		setOnlineStatus,
+		setUpdateAvailable,
+		syncInstallHelpState
+	} from '$lib/pwa';
 
 	let { children } = $props();
 
@@ -22,20 +29,37 @@
 		const handleBeforeInstallPrompt = (event) => {
 			event.preventDefault();
 			setInstallPrompt(event);
+			syncInstallHelpState();
 		};
 
 		const handleAppInstalled = () => {
 			clearInstallPrompt();
+			syncInstallHelpState();
 		};
 
+		const handleOnline = () => {
+			setOnlineStatus(true);
+		};
+
+		const handleOffline = () => {
+			setOnlineStatus(false);
+		};
+
+		setOnlineStatus(navigator.onLine);
+		syncInstallHelpState();
+
 		window.addEventListener('beforeinstallprompt', handleBeforeInstallPrompt);
 		window.addEventListener('appinstalled', handleAppInstalled);
+		window.addEventListener('online', handleOnline);
+		window.addEventListener('offline', handleOffline);
 
 		void appController.init();
 
 		return () => {
 			window.removeEventListener('beforeinstallprompt', handleBeforeInstallPrompt);
 			window.removeEventListener('appinstalled', handleAppInstalled);
+			window.removeEventListener('online', handleOnline);
+			window.removeEventListener('offline', handleOffline);
 			void appController.destroy();
 		};
 	});