feat(frontend): replace all name concatenation with displayName

- Add displayName default method to PersonSummaryDTO
- Update native SQL queries to include title, person_type columns
- Add getInitials() utility to personFormat.ts
- Update abbreviateName/abbreviateCompact for nullable firstName
- Replace firstName+lastName concatenation with displayName in all
  person-displaying components and server load files
- Regenerate API types with displayName on Person and PersonSummaryDTO

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

frontend/src/lib/components/DashboardRecentDocuments.svelte

@@ -7,7 +7,7 @@ type Document = {
 	id: string;
 	title: string;
 	updatedAt?: string;
-	sender?: { id: string; firstName: string; lastName: string };
+	sender?: { id: string; firstName?: string | null; lastName: string; displayName: string };
 };
 
 type StatsDTO = components['schemas']['StatsDTO'];