fix(review): address reviewer concerns from PR #661

- Replace brittle createdAt===updatedAt isNew() check with a 7-day
  recency window (created within last 7 days = new)
- Add createdAt/updatedAt to searchItem fixture in page.server.spec.ts
  and assert they are propagated to recentDocs
- Replace null timestamps in DocumentListItem test fixtures with a fixed
  LocalDateTime to satisfy the @Schema(required) contract

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

frontend/src/lib/shared/dashboard/ReaderRecentDocs.svelte

@@ -12,7 +12,7 @@ interface Props {
 const { documents }: Props = $props();
 
 function isNew(doc: DocumentListItem): boolean {
-	return new Date(doc.createdAt).getTime() === new Date(doc.updatedAt).getTime();
+	return new Date(doc.createdAt).getTime() > Date.now() - 7 * 24 * 60 * 60 * 1000;
 }
 </script>