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/documents/[id]/edit/+page.svelte

@@ -54,7 +54,7 @@ let selectedReceivers = $state(doc.receivers ?? []);
 			bind:selectedReceivers={selectedReceivers}
 			initialDateIso={doc.documentDate ?? ''}
 			initialLocation={doc.location ?? ''}
-			initialSenderName={doc.sender ? `${doc.sender.firstName} ${doc.sender.lastName}` : ''}
+			initialSenderName={doc.sender ? doc.sender.displayName : ''}
 		/>
 		<DescriptionSection
 			bind:tags={tags}

frontend/src/routes/documents/new/+page.server.ts

@@ -24,14 +24,19 @@ export async function load({
 	const api = createApiClient(fetch);
 
 	let initialSenderName = '';
-	let initialReceivers: { id: string; firstName: string; lastName: string }[] = [];
+	let initialReceivers: {
+		id: string;
+		firstName?: string;
+		lastName: string;
+		displayName: string;
+	}[] = [];
 
 	const requests: Promise<void>[] = [];
 
 	if (senderId) {
 		requests.push(
 			api.GET('/api/persons/{id}', { params: { path: { id: senderId } } }).then(({ data }) => {
-				if (data) initialSenderName = `${data.firstName} ${data.lastName}`;
+				if (data) initialSenderName = data.displayName;
 			})
 		);
 	}
@@ -40,7 +45,14 @@ export async function load({
 		requests.push(
 			api.GET('/api/persons/{id}', { params: { path: { id: receiverId } } }).then(({ data }) => {
 				if (data)
-					initialReceivers = [{ id: data.id!, firstName: data.firstName, lastName: data.lastName }];
+					initialReceivers = [
+						{
+							id: data.id!,
+							firstName: data.firstName,
+							lastName: data.lastName,
+							displayName: data.displayName
+						}
+					];
 			})
 		);
 	}

frontend/src/routes/documents/new/+page.svelte

@@ -12,9 +12,8 @@ let { data, form } = $props();
 
 let tags: string[] = $state([]);
 let senderId = $state(untrack(() => data.initialSenderId));
-let selectedReceivers: { id: string; firstName: string; lastName: string }[] = $state(
-	untrack(() => data.initialReceivers)
-);
+let selectedReceivers: { id: string; firstName?: string; lastName: string; displayName: string }[] =
+	$state(untrack(() => data.initialReceivers));
 
 let parsedSuggestion = $state<FilenameParseResult>({});