feat(ui): Create content pattern components - DataTable, FilterBar, EmptyState, LoadingState

- Add LoadingState with table, card, list, and text skeleton patterns
- Add EmptyState with customizable icon, title, description, and action slot
- Add FilterBar with search input, clear button, and custom filter slot
- Add DataTable with TanStack Table integration, sorting, and row click
- Create barrel export index.ts for common components
- Install tanstack-table-8-svelte-5 for Svelte 5 compatibility
- Sync auth spec with authenticated user redirect requirements
- Archive p03-dashboard-enhancement

Refs: openspec/changes/p04-content-patterns
Closes: p04-content-patterns

frontend/src/lib/components/common/EmptyState.svelte

@@ -0,0 +1,32 @@
+<script lang="ts">
+	import { Inbox } from 'lucide-svelte';
+	import type { Snippet } from 'svelte';
+	import type { ComponentType, SvelteComponent } from 'svelte';
+
+	interface Props {
+		title?: string;
+		description?: string;
+		icon?: ComponentType<SvelteComponent>;
+		children?: Snippet;
+	}
+
+	let { 
+		title = 'No data', 
+		description = 'No records found.',
+		icon: Icon = Inbox,
+		children 
+	}: Props = $props();
+</script>
+
+<div class="empty-state flex flex-col items-center justify-center py-12 text-center">
+	<div class="text-base-content/30 mb-4">
+		<svelte:component this={Icon} size={48} />
+	</div>
+	<h3 class="text-lg font-medium text-base-content/70">{title}</h3>
+	<p class="text-sm text-base-content/50 mt-1 max-w-sm">{description}</p>
+	{#if children}
+		<div class="mt-4">
+			{@render children()}
+		</div>
+	{/if}
+</div>