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/settings/+page.svelte

@@ -1,4 +1,5 @@
 <script lang="ts">
+	import { t } from 'svelte-i18n';
 	import type { PageData } from './$types.js';
 	import SettingsForm from '$lib/components/admin/SettingsForm.svelte';
 
@@ -6,13 +7,13 @@
 </script>
 
 <svelte:head>
-	<title>System Settings — Admin</title>
+	<title>{$t('admin.system_settings')} — {$t('admin.panel')}</title>
 </svelte:head>
 
 <div>
 	<div class="mb-6">
-		<h1 class="text-2xl font-bold text-card-foreground">System Settings</h1>
-		<p class="mt-1 text-sm text-muted-foreground">Configure global application settings.</p>
+		<h1 class="text-2xl font-bold text-card-foreground">{$t('admin.system_settings')}</h1>
+		<p class="mt-1 text-sm text-muted-foreground">{$t('admin.settings_description')}</p>
 	</div>
 
 	<SettingsForm form={data.form} />