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]/PersonCard.svelte

@@ -8,8 +8,9 @@ let {
 }: {
 	person: {
 		id: string;
-		firstName: string;
+		firstName?: string | null;
 		lastName: string;
+		displayName: string;
 		alias?: string | null;
 		birthYear?: number | null;
 		deathYear?: number | null;
@@ -29,14 +30,13 @@ let {
 			<div
 				class="flex h-16 w-16 items-center justify-center rounded-full bg-primary font-serif text-xl font-bold text-primary-fg"
 			>
-				{person.firstName[0]}{person.lastName[0]}
+				{person.firstName ? person.firstName[0] : person.lastName[0]}{person.lastName[0]}
 			</div>
 		</div>
 
 		<!-- Name — centered, serif -->
 		<h1 class="mb-1 text-center font-serif text-xl font-bold text-ink">
-			{person.firstName}
-			{person.lastName}
+			{person.displayName}
 		</h1>
 
 		<!-- Alias — centered, italic -->