feat(#145): switch dashboard to show last-activity documents

Replace recent-by-creation fetch with GET /api/documents/recent-activity
(sorted by updatedAt) in the dashboard. Update DashboardRecentDocuments
component to use doc.updatedAt, update i18n heading to "Zuletzt aktiv" /
"Recent Activity" / "Actividad reciente", and regenerate API types.

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

frontend/src/lib/components/DashboardRecentDocuments.svelte

@@ -5,7 +5,7 @@ import { getLocale } from '$lib/paraglide/runtime.js';
 type Document = {
 	id: string;
 	title: string;
-	createdAt?: string;
+	updatedAt?: string;
 	sender?: { id: string; firstName: string; lastName: string };
 };
 
@@ -37,12 +37,12 @@ function formatDate(dateStr: string): string {
 				>
 					{doc.title}
 				</a>
-				{#if doc.createdAt}
+				{#if doc.updatedAt}
 					<span
 						data-testid="doc-date-{doc.id}"
 						class="ml-2 shrink-0 font-sans text-xs text-gray-400"
 					>
-						{formatDate(doc.createdAt)}
+						{formatDate(doc.updatedAt)}
 					</span>
 				{/if}
 			</div>

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

@@ -9,12 +9,12 @@ afterEach(cleanup);
 type Document = {
 	id: string;
 	title: string;
-	createdAt?: string;
+	updatedAt?: string;
 	sender?: { id: string; firstName: string; lastName: string };
 };
 
-function makeDoc(id: string, title: string, createdAt?: string): Document {
-	return { id, title, createdAt };
+function makeDoc(id: string, title: string, updatedAt?: string): Document {
+	return { id, title, updatedAt };
 }
 
 describe('DashboardRecentDocuments', () => {