feat(#145): add DashboardRecentDocuments widget component

Shows recently reviewed documents as a dashboard widget with formatted
dates. Renders nothing when the list is empty.

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

frontend/src/lib/components/DashboardRecentDocuments.svelte

@@ -0,0 +1,48 @@
+<script lang="ts">
+type Document = {
+	id: string;
+	title: string;
+	documentDate?: string;
+	sender?: { id: string; firstName: string; lastName: string };
+};
+
+interface Props {
+	recentDocs: Document[];
+}
+
+let { recentDocs }: Props = $props();
+
+function formatDate(dateStr: string): string {
+	return new Intl.DateTimeFormat('de-DE', {
+		day: 'numeric',
+		month: 'long',
+		year: 'numeric'
+	}).format(new Date(dateStr + 'T12:00:00'));
+}
+</script>
+
+{#if recentDocs.length > 0}
+	<div data-testid="dashboard-recent-docs" class="border-brand-sand rounded-sm border bg-white p-6">
+		<h2 class="mb-4 font-sans text-xs font-bold tracking-widest text-gray-400 uppercase">
+			Zuletzt hinzugefügt
+		</h2>
+		{#each recentDocs as doc (doc.id)}
+			<div class="border-brand-sand flex items-center justify-between border-b py-2 last:border-0">
+				<a
+					href="/documents/{doc.id}"
+					class="font-serif text-sm text-ink hover:text-brand-navy hover:underline"
+				>
+					{doc.title}
+				</a>
+				{#if doc.documentDate}
+					<span
+						data-testid="doc-date-{doc.id}"
+						class="ml-2 shrink-0 font-sans text-xs text-gray-400"
+					>
+						{formatDate(doc.documentDate)}
+					</span>
+				{/if}
+			</div>
+		{/each}
+	</div>
+{/if}