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/lib/components/layout/InstallPrompt.svelte

@@ -0,0 +1,103 @@
+<script lang="ts">
+	import { t } from 'svelte-i18n';
+	import { browser } from '$app/environment';
+	import { Download, X } from 'lucide-svelte';
+	import { fade } from 'svelte/transition';
+
+	const DISMISS_KEY = 'wal-install-prompt-dismissed';
+
+	interface BeforeInstallPromptEvent extends Event {
+		prompt(): Promise<void>;
+		userChoice: Promise<{ outcome: 'accepted' | 'dismissed' }>;
+	}
+
+	let deferredPrompt: BeforeInstallPromptEvent | null = $state(null);
+	let dismissed = $state(false);
+	let installed = $state(false);
+
+	const visible = $derived(deferredPrompt !== null && !dismissed && !installed);
+
+	function isDismissed(): boolean {
+		if (!browser) return false;
+		try {
+			return localStorage.getItem(DISMISS_KEY) === 'true';
+		} catch {
+			return false;
+		}
+	}
+
+	function dismiss() {
+		dismissed = true;
+		if (browser) {
+			try {
+				localStorage.setItem(DISMISS_KEY, 'true');
+			} catch {
+				// localStorage unavailable
+			}
+		}
+	}
+
+	async function install() {
+		if (!deferredPrompt) return;
+
+		await deferredPrompt.prompt();
+		const { outcome } = await deferredPrompt.userChoice;
+
+		if (outcome === 'accepted') {
+			installed = true;
+		}
+		deferredPrompt = null;
+	}
+
+	if (browser) {
+		dismissed = isDismissed();
+
+		window.addEventListener('beforeinstallprompt', (e: Event) => {
+			e.preventDefault();
+			deferredPrompt = e as BeforeInstallPromptEvent;
+		});
+
+		window.addEventListener('appinstalled', () => {
+			installed = true;
+			deferredPrompt = null;
+		});
+	}
+</script>
+
+{#if visible}
+	<div
+		transition:fade={{ duration: 200 }}
+		class="fixed bottom-4 left-4 right-4 z-50 mx-auto flex max-w-lg items-center gap-3 rounded-xl border border-border bg-card p-4 shadow-lg"
+		role="alert"
+	>
+		<div class="flex h-10 w-10 shrink-0 items-center justify-center rounded-lg bg-primary/10">
+			<Download class="h-5 w-5 text-primary" />
+		</div>
+
+		<div class="min-w-0 flex-1">
+			<p class="text-sm font-medium text-foreground">
+				{$t('install.title')}
+			</p>
+			<p class="text-xs text-muted-foreground">
+				{$t('install.description')}
+			</p>
+		</div>
+
+		<button
+			type="button"
+			onclick={install}
+			class="shrink-0 rounded-lg bg-primary px-4 py-2 text-sm font-medium text-primary-foreground transition-colors hover:bg-primary/90"
+		>
+			{$t('install.button')}
+		</button>
+
+		<button
+			type="button"
+			onclick={dismiss}
+			class="shrink-0 rounded-md p-1 text-muted-foreground transition-colors hover:bg-muted hover:text-foreground"
+			aria-label={$t('install.dismiss')}
+		>
+			<X class="h-4 w-4" />
+		</button>
+	</div>
+{/if}

src/lib/components/layout/MainLayout.svelte

@@ -3,6 +3,7 @@
 	import type { Snippet } from 'svelte';
 	import Sidebar from './Sidebar.svelte';
 	import Header from './Header.svelte';
+	import InstallPrompt from './InstallPrompt.svelte';
 	import AmbientBackground from '$lib/components/background/AmbientBackground.svelte';
 	import SearchDialog from '$lib/components/search/SearchDialog.svelte';
 	import { ui } from '$lib/stores/ui.svelte.js';
@@ -66,3 +67,6 @@
 
 <!-- Search Dialog (modal, z-50) -->
 <SearchDialog />
+
+<!-- PWA Install Prompt -->
+<InstallPrompt />