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/DocumentMetadataDrawer.svelte

@@ -2,9 +2,9 @@
 import { m } from '$lib/paraglide/messages.js';
 import { formatDate } from '$lib/utils/date';
 import { formatDocumentStatus } from '$lib/utils/documentStatusLabel';
-import { personAvatarColor } from '$lib/utils/personFormat';
+import { getInitials as calcInitials, personAvatarColor } from '$lib/utils/personFormat';
 
-type Person = { id: string; firstName: string; lastName: string };
+type Person = { id: string; firstName?: string | null; lastName: string; displayName: string };
 type Tag = { id: string; name: string };
 
 type Props = {
@@ -33,11 +33,11 @@ let showAllReceivers = $state(false);
 const displayedReceivers = $derived(showAllReceivers ? receivers : visibleReceivers);
 
 function getInitials(person: Person): string {
-	return `${person.firstName.charAt(0)}${person.lastName.charAt(0)}`.toUpperCase();
+	return calcInitials(person);
 }
 
 function getFullName(person: Person): string {
-	return `${person.firstName} ${person.lastName}`;
+	return person.displayName;
 }
 </script>