feat(notify-bridge): phase 7 - frontend restructuring

Notify Bridge frontend with SvelteKit 2 + Svelte 5 + Tailwind CSS v4:
- Auth: login page, setup page, auth state management with $state runes
- Theme: dark/light toggle with localStorage persistence
- i18n: EN/RU translations with reactive $state-based t() function
- Routes: dashboard, providers, trackers, targets, tracking-configs,
  template-configs, telegram-bots, users (stubs for configs pages)
- Providers page: list with card grid, "Add Provider" button
- API client: JWT auth, auto-redirect on 401, typed request helpers
- Branding: "Notify Bridge" throughout, Observatory theme colors

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/routes/+page.svelte

@@ -1,9 +1,18 @@
 <script>
+	import { t } from '$lib/i18n/index.svelte.ts';
 </script>
 
 <div class="min-h-screen flex items-center justify-center">
-	<div class="text-center">
-		<h1 class="text-4xl font-bold text-foreground mb-2">Notify Bridge</h1>
-		<p class="text-muted-foreground">Service-to-notification bridge</p>
+	<div class="text-center animate-fade-slide-in">
+		<h1 class="text-5xl font-bold text-foreground mb-3">{t('app.name')}</h1>
+		<p class="text-lg text-muted-foreground mb-8">{t('app.tagline')}</p>
+		<div class="flex gap-4 justify-center">
+			<a href="/login" class="px-6 py-3 bg-primary text-primary-foreground rounded-[var(--radius)] font-medium hover:opacity-90 transition-opacity">
+				{t('auth.login')}
+			</a>
+			<a href="/providers" class="px-6 py-3 bg-muted text-foreground rounded-[var(--radius)] font-medium hover:bg-accent transition-colors">
+				{t('nav.providers')}
+			</a>
+		</div>
 	</div>
 </div>