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]/edit/+page.svelte

@@ -30,8 +30,7 @@ const person = $derived(data.person);
 					d="M10 19l-7-7m0 0l7-7m-7 7h18"
 				/>
 			</svg>
-			{person.firstName}
-			{person.lastName}
+			{person.displayName}
 		</a>
 		<h1 class="font-serif text-3xl text-ink">{m.person_edit_heading()}</h1>
 	</div>

frontend/src/routes/persons/[id]/edit/PersonDangerZone.svelte

@@ -6,7 +6,7 @@ let {
 	person,
 	form
 }: {
-	person: { id: string; firstName: string; lastName: string };
+	person: { id: string; firstName?: string | null; lastName: string; displayName: string };
 	form?: { mergeError?: string } | null;
 } = $props();
 

frontend/src/routes/persons/[id]/edit/PersonEditForm.svelte

@@ -5,7 +5,7 @@ let {
 	person
 }: {
 	person: {
-		firstName: string;
+		firstName?: string | null;
 		lastName: string;
 		alias?: string | null;
 		birthYear?: number | null;