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/OverflowPillButton.svelte

@@ -3,7 +3,7 @@ import { tick } from 'svelte';
 import { m } from '$lib/paraglide/messages.js';
 import { clickOutside } from '$lib/actions/clickOutside';
 
-type Person = { id: string; firstName: string; lastName: string };
+type Person = { id: string; firstName?: string | null; lastName: string; displayName: string };
 
 type Props = {
 	extraCount: number;
@@ -67,8 +67,7 @@ function handleKeydown(e: KeyboardEvent) {
 						href="/persons/{person.id}"
 						class="block py-0.5 text-[18px] text-ink hover:text-primary focus-visible:ring-2 focus-visible:ring-primary"
 					>
-						{person.firstName}
-						{person.lastName}
+						{person.displayName}
 					</a>
 				</div>
 			{/each}