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/layout/LanguageSwitcher.svelte

@@ -0,0 +1,19 @@
+<script lang="ts">
+	import { locale } from 'svelte-i18n';
+	import { storeLocale } from '$lib/i18n/index.js';
+
+	function toggleLocale() {
+		const next = $locale === 'ru' ? 'en' : 'ru';
+		locale.set(next);
+		storeLocale(next);
+	}
+</script>
+
+<button
+	type="button"
+	onclick={toggleLocale}
+	class="inline-flex items-center justify-center rounded-md px-2 py-1.5 text-xs font-medium text-muted-foreground transition-colors hover:bg-accent hover:text-foreground focus:outline-none focus:ring-2 focus:ring-ring"
+	title={$locale === 'ru' ? 'Switch to English' : 'Переключить на русский'}
+>
+	{$locale === 'ru' ? 'RU' : 'EN'}
+</button>