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/+page.svelte

@@ -99,13 +99,12 @@ function handleSearch() {
 						<div
 							class="flex h-12 w-12 flex-shrink-0 items-center justify-center rounded-full bg-primary font-serif text-base font-bold text-primary-fg transition-colors"
 						>
-							{person.firstName?.[0]}{person.lastName?.[0]}
+							{person.firstName ? person.firstName[0] : person.lastName[0]}{person.lastName[0]}
 						</div>
 
 						<!-- Name -->
 						<p class="font-serif text-sm font-bold text-ink group-hover:underline">
-							{person.firstName}
-							{person.lastName}
+							{person.displayName}
 						</p>
 
 						<!-- Alias -->

frontend/src/routes/persons/[id]/+page.svelte

@@ -23,7 +23,7 @@ const coCorrespondents = $derived.by(() => {
 			else
 				freq.set(key, {
 					id: receiver.id,
-					name: `${receiver.firstName} ${receiver.lastName}`,
+					name: receiver.displayName,
 					count: 1
 				});
 		}
@@ -37,7 +37,7 @@ const coCorrespondents = $derived.by(() => {
 			else
 				freq.set(key, {
 					id: doc.sender.id,
-					name: `${doc.sender.firstName} ${doc.sender.lastName}`,
+					name: doc.sender.displayName,
 					count: 1
 				});
 		}

frontend/src/routes/persons/[id]/NameHistoryCard.svelte

@@ -9,7 +9,7 @@ interface Props {
 		type: string;
 		sortOrder: number;
 	}>;
-	personFirstName: string;
+	personFirstName?: string | null;
 }
 
 let { aliases, personFirstName }: Props = $props();

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 -->

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}

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;