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/lib/components/board/DraggableBoard.svelte

@@ -1,4 +1,5 @@
 <script lang="ts">
+	import { t } from 'svelte-i18n';
 	import { dndzone } from 'svelte-dnd-action';
 	import DraggableSection from '$lib/components/section/DraggableSection.svelte';
 
@@ -36,7 +37,7 @@
 		addWidgetSectionId: string | null;
 		onToggleAddWidget: (sectionId: string) => void;
 		onDeleteSection: (sectionId: string) => void;
-		onAddWidget: (sectionId: string, appId: string) => void;
+		onAddWidget: (sectionId: string, widgetData: string) => void;
 		onDeleteWidget: (widgetId: string) => void;
 	}
 
@@ -99,7 +100,7 @@
 
 {#if sections.length === 0}
 	<div class="rounded-xl border border-border bg-card/50 p-8 text-center">
-		<p class="text-muted-foreground">No sections yet. Add one to get started.</p>
+		<p class="text-muted-foreground">{$t('board.no_sections')}</p>
 	</div>
 {:else}
 	<div