feat(shopping): add ShoppingHeader.svelte component

Displays title, eyebrow counts (remaining/checked), generation
timestamp, and planner-only generate/regenerate button.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/lib/shopping/ShoppingHeader.svelte

@@ -0,0 +1,58 @@
+<script lang="ts">
+	import { enhance } from '$app/forms';
+
+	interface Props {
+		totalItems: number;
+		checkedCount: number;
+		generatedAt: string | null;
+		weekPlanId: string | null;
+		isPlanner: boolean;
+		hasShoppingList: boolean;
+	}
+
+	let { totalItems, checkedCount, generatedAt, weekPlanId, isPlanner, hasShoppingList }: Props = $props();
+
+	let remainingCount = $derived(totalItems - checkedCount);
+
+	let formattedTime = $derived(
+		generatedAt
+			? new Date(generatedAt).toLocaleString('de-DE', {
+					day: '2-digit',
+					month: '2-digit',
+					hour: '2-digit',
+					minute: '2-digit'
+				})
+			: null
+	);
+</script>
+
+<header class="flex flex-col gap-1">
+	<div class="flex items-center justify-between">
+		<h1 class="font-[var(--font-display)] text-[20px] font-[300] text-[var(--color-text)]">
+			Einkaufsliste
+		</h1>
+
+		{#if isPlanner && weekPlanId}
+			<form method="POST" action="?/generate" use:enhance>
+				<input type="hidden" name="weekPlanId" value={weekPlanId} />
+				<button
+					type="submit"
+					class="rounded-[var(--radius-md)] {hasShoppingList
+						? 'border border-[var(--color-border)] text-[var(--color-text)] hover:bg-[var(--color-surface)]'
+						: 'bg-[var(--green-dark)] text-white'} px-3 py-1.5 text-[13px] font-medium tracking-[0.04em] font-[var(--font-sans)]"
+				>
+					{hasShoppingList ? 'Neu generieren' : 'Liste generieren'}
+				</button>
+			</form>
+		{/if}
+	</div>
+
+	{#if hasShoppingList}
+		<p class="font-[var(--font-sans)] text-[12px] text-[var(--color-text-muted)]">
+			{remainingCount} Artikel übrig · {checkedCount} abgehakt
+			{#if formattedTime}
+				<span class="ml-1">· erstellt {formattedTime}</span>
+			{/if}
+		</p>
+	{/if}
+</header>