feat(#145): add DashboardResumeStrip component

- Component reads familienarchiv.lastVisited from localStorage and
  shows a 'Zuletzt geöffnet' link to the last-visited document
- Renders nothing when no localStorage entry exists
- Document detail page writes id+title to localStorage on mount

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

frontend/src/lib/components/DashboardResumeStrip.svelte

@@ -0,0 +1,36 @@
+<script lang="ts">
+import { onMount } from 'svelte';
+
+interface LastVisited {
+	id: string;
+	title: string;
+}
+
+let lastVisited = $state<LastVisited | null>(null);
+
+onMount(() => {
+	try {
+		const raw = localStorage.getItem('familienarchiv.lastVisited');
+		if (raw) {
+			const parsed = JSON.parse(raw) as LastVisited;
+			if (parsed?.id) {
+				lastVisited = parsed;
+			}
+		}
+	} catch {
+		// ignore malformed JSON
+	}
+});
+</script>
+
+{#if lastVisited}
+	<div
+		data-testid="resume-strip"
+		class="border-brand-sand flex items-center gap-2 rounded-sm border bg-white px-4 py-3 font-sans text-sm"
+	>
+		<span class="text-gray-500">Zuletzt geöffnet:</span>
+		<a href="/documents/{lastVisited.id}" class="font-medium text-brand-navy hover:underline">
+			{lastVisited.title || 'Zuletzt geöffnet'}
+		</a>
+	</div>
+{/if}