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/persons/[id]/PersonMergePanel.svelte

@@ -7,7 +7,7 @@ let {
 	person,
 	form
 }: {
-	person: { firstName: string; lastName: string };
+	person: { displayName: string };
 	form?: { mergeError?: string } | null;
 } = $props();
 
@@ -74,7 +74,7 @@ let showMergeConfirm = $state(false);
 
 			{#if showMergeConfirm}
 				<p class="mt-3 rounded border border-red-200 bg-red-50 px-3 py-2 text-sm text-red-700">
-					{m.person_merge_warning()} <strong>{person.firstName} {person.lastName}</strong>
+					{m.person_merge_warning()} <strong>{person.displayName}</strong>
 					{m.person_merge_will_be_deleted()}
 				</p>
 			{/if}