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}

frontend/src/lib/components/DashboardResumeStrip.svelte.spec.ts

@@ -0,0 +1,43 @@
+import { describe, it, expect, afterEach } from 'vitest';
+import { cleanup, render } from 'vitest-browser-svelte';
+import { page } from 'vitest/browser';
+
+import DashboardResumeStrip from './DashboardResumeStrip.svelte';
+
+afterEach(() => {
+	cleanup();
+	localStorage.clear();
+});
+
+describe('DashboardResumeStrip', () => {
+	it('renders nothing when no last-visited document in localStorage', async () => {
+		render(DashboardResumeStrip, {});
+		const strip = page.getByTestId('resume-strip');
+		await expect.element(strip).not.toBeInTheDocument();
+	});
+
+	it('shows the strip with link when localStorage has a document', async () => {
+		localStorage.setItem(
+			'familienarchiv.lastVisited',
+			JSON.stringify({ id: 'doc-123', title: 'Geburtsurkunde 1920' })
+		);
+		render(DashboardResumeStrip, {});
+		const strip = page.getByTestId('resume-strip');
+		await expect.element(strip).toBeInTheDocument();
+		const link = page.getByRole('link', { name: /Geburtsurkunde 1920/ });
+		await expect.element(link).toBeInTheDocument();
+		await expect.element(link).toHaveAttribute('href', '/documents/doc-123');
+	});
+
+	it('uses title fallback text when title is empty', async () => {
+		localStorage.setItem(
+			'familienarchiv.lastVisited',
+			JSON.stringify({ id: 'doc-456', title: '' })
+		);
+		render(DashboardResumeStrip, {});
+		const strip = page.getByTestId('resume-strip');
+		await expect.element(strip).toBeInTheDocument();
+		const link = page.getByRole('link');
+		await expect.element(link).toHaveAttribute('href', '/documents/doc-456');
+	});
+});

frontend/src/routes/documents/[id]/+page.svelte

@@ -113,6 +113,14 @@ onMount(() => {
 
 	localStorageRestored = true;
 
+	// Track last-visited document for the dashboard resume strip
+	if (doc?.id) {
+		localStorage.setItem(
+			'familienarchiv.lastVisited',
+			JSON.stringify({ id: doc.id, title: doc.title ?? '' })
+		);
+	}
+
 	function onKeyDown(e: KeyboardEvent) {
 		if (e.key === 'Escape') {
 			if (activeAnnotationId) {