Add SvelteKit frontend with Tailwind CSS (Phase 4)

Build a modern, calm web UI using SvelteKit 5 + Tailwind CSS v4.

Pages:
- Setup wizard (first-run admin account creation)
- Login with JWT token management and auto-refresh
- Dashboard with stats cards and recent events timeline
- Servers: add/delete Immich server connections with validation
- Trackers: create album trackers with album picker, event type
  selection, target assignment, and scan interval config
- Templates: Jinja2 message template editor with live preview
- Targets: Telegram and webhook notification targets with test
- Users: admin-only user management (create/delete)

Architecture:
- Reactive auth state with Svelte 5 runes
- API client with JWT auth, auto-refresh on 401
- Static adapter builds to 153KB for embedding in FastAPI
- Vite proxy config for dev server -> backend API
- Sidebar layout with navigation and user info

Also adds Rule 2 to primary plan: perform detailed code review
after completing each phase.

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

frontend/src/lib/components/PageHeader.svelte

@@ -0,0 +1,19 @@
+<script lang="ts">
+	let { title, description = '', children } = $props<{
+		title: string;
+		description?: string;
+		children?: import('svelte').Snippet;
+	}>();
+</script>
+
+<div class="flex items-center justify-between mb-6">
+	<div>
+		<h2 class="text-2xl font-semibold tracking-tight">{title}</h2>
+		{#if description}
+			<p class="text-sm text-[var(--color-muted-foreground)] mt-1">{description}</p>
+		{/if}
+	</div>
+	{#if children}
+		{@render children()}
+	{/if}
+</div>