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/documents/[id]/edit/+page.svelte

@@ -54,7 +54,7 @@ let selectedReceivers = $state(doc.receivers ?? []);
 			bind:selectedReceivers={selectedReceivers}
 			initialDateIso={doc.documentDate ?? ''}
 			initialLocation={doc.location ?? ''}
-			initialSenderName={doc.sender ? `${doc.sender.firstName} ${doc.sender.lastName}` : ''}
+			initialSenderName={doc.sender ? doc.sender.displayName : ''}
 		/>
 		<DescriptionSection
 			bind:tags={tags}