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/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 />