feat(phase3): PWA, auto-discovery, bookmarklet, multi-tab sync

- PWA: manifest, service worker (cache-first static, network-first API),
  offline page, install prompt banner
- Auto-discovery: Docker socket + Traefik API scanning, approval UI
- Quick-add bookmarklet: popup-based add page, favicon auto-detect
- Multi-tab sync: BroadcastChannel for theme + data changes
- i18n translations for all new strings (EN/RU)

src/routes/offline/+page.svelte

@@ -0,0 +1,38 @@
+<script lang="ts">
+	import { t } from 'svelte-i18n';
+	import { WifiOff, RefreshCw } from 'lucide-svelte';
+
+	function retry() {
+		window.location.reload();
+	}
+</script>
+
+<svelte:head>
+	<title>{$t('offline.title')}</title>
+</svelte:head>
+
+<div class="flex min-h-[60vh] flex-col items-center justify-center gap-6 px-4 text-center">
+	<div
+		class="flex h-20 w-20 items-center justify-center rounded-full bg-muted"
+	>
+		<WifiOff class="h-10 w-10 text-muted-foreground" />
+	</div>
+
+	<div class="space-y-2">
+		<h1 class="text-2xl font-bold text-foreground">
+			{$t('offline.title')}
+		</h1>
+		<p class="max-w-md text-muted-foreground">
+			{$t('offline.description')}
+		</p>
+	</div>
+
+	<button
+		type="button"
+		onclick={retry}
+		class="inline-flex items-center gap-2 rounded-lg bg-primary px-6 py-3 text-sm font-medium text-primary-foreground transition-colors hover:bg-primary/90"
+	>
+		<RefreshCw class="h-4 w-4" />
+		{$t('offline.retry')}
+	</button>
+</div>