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/routes/enrich/[id]/+page.svelte

@@ -120,7 +120,7 @@ let selectedReceivers = $state(untrack(() => doc.receivers ?? []));
 					initialDateIso={doc.documentDate ?? ''}
 					initialLocation={doc.location ?? ''}
 					initialSenderName={doc.sender
-						? `${doc.sender.firstName} ${doc.sender.lastName}`
+						? doc.sender.displayName
 						: ''}
 				/>
 				<DescriptionSection bind:tags={tags} initialTitle={doc.title ?? ''} titleRequired={true} />