feat: port original frontend UI to Notify Bridge

Port the full polished frontend from Immich Watcher:
- Sidebar layout with collapsible nav, mobile bottom nav
- Login/setup pages with gradient mesh background, animations
- 11 reusable components: Card, Modal, ConfirmModal, Snackbar,
  IconPicker, JinjaEditor, MdiIcon, PageHeader, Loading, Hint, IconButton
- Auth state with getAuth() reactive pattern, token refresh
- Theme: light/dark/system with media query listener
- i18n: EN/RU with nested JSON, auto-detect locale
- Snackbar notification store

Branding changes:
- "Immich Watcher" -> "Notify Bridge"
- /servers -> /providers in nav and routes
- Login icon: mdiEye -> mdiLan

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

frontend/src/routes/+page.svelte

@@ -1,18 +1,13 @@
-<script>
-	import { t } from '$lib/i18n/index.svelte.ts';
+<script lang="ts">
+	import { t } from '$lib/i18n';
+	import { getAuth } from '$lib/auth.svelte';
+	import PageHeader from '$lib/components/PageHeader.svelte';
+
+	const auth = getAuth();
 </script>
 
-<div class="min-h-screen flex items-center justify-center">
-	<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>
+<PageHeader title={t('dashboard.title')} description={t('dashboard.description')} />
+
+<div class="text-center py-12">
+	<p class="text-muted-foreground">{t('dashboard.noEvents')}</p>
 </div>