feat(phase2): localization EN/RU + additional widget types

- Add svelte-i18n with 224 translation keys (English + Russian)
- Language switcher in header (EN/RU toggle, persists to localStorage)
- Extract all hardcoded strings from 37 component/page files
- Add 4 new widget types: Bookmark, Note (markdown), Embed (iframe), Status
- WidgetRenderer dispatches by type, WidgetGrid supports full-width widgets
- Type-specific config forms in board editor
- Install marked for markdown rendering

src/routes/admin/+layout.svelte

@@ -1,15 +1,16 @@
 <script lang="ts">
+	import { t } from 'svelte-i18n';
 	import type { Snippet } from 'svelte';
 	import type { LayoutData } from './$types.js';
 	import { page } from '$app/stores';
 
 	let { data, children }: { data: LayoutData; children: Snippet } = $props();
 
-	const navItems = [
-		{ href: '/admin/users', label: 'Users' },
-		{ href: '/admin/groups', label: 'Groups' },
-		{ href: '/admin/settings', label: 'Settings' }
-	] as const;
+	const navItems = $derived([
+		{ href: '/admin/users', labelKey: 'admin.users' },
+		{ href: '/admin/groups', labelKey: 'admin.groups' },
+		{ href: '/admin/settings', labelKey: 'admin.settings' }
+	]);
 
 	function isActive(href: string): boolean {
 		return $page.url.pathname === href;
@@ -20,7 +21,7 @@
 	<div class="mx-auto max-w-6xl">
 		<!-- Admin header -->
 		<div class="mb-6 flex flex-wrap items-center gap-4 rounded-xl border border-border bg-card p-4 shadow-sm">
-			<span class="text-sm font-semibold text-foreground">Admin Panel</span>
+			<span class="text-sm font-semibold text-foreground">{$t('admin.panel')}</span>
 			<div class="flex gap-1">
 				{#each navItems as item (item.href)}
 					<a
@@ -29,12 +30,12 @@
 							? 'bg-primary text-primary-foreground'
 							: 'text-muted-foreground hover:bg-accent hover:text-foreground'}"
 					>
-						{item.label}
+						{$t(item.labelKey)}
 					</a>
 				{/each}
 			</div>
 			<div class="ml-auto text-xs text-muted-foreground">
-				{data.user.displayName} (admin)
+				{data.user.displayName} ({$t('admin.role_admin').toLowerCase()})
 			</div>
 		</div>