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/+layout.svelte

@@ -1,5 +1,6 @@
 <script lang="ts">
 	import '../app.css';
+	import '$lib/i18n/index.js';
 	import type { Snippet } from 'svelte';
 	import type { LayoutData } from './$types.js';
 	import MainLayout from '$lib/components/layout/MainLayout.svelte';