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/briefwechsel/+page.server.ts

@@ -52,8 +52,8 @@ export async function load({ url, fetch, locals }) {
 					const code = (result.error as unknown as { code?: string })?.code;
 					throw error(result.response.status, getErrorMessage(code));
 				}
-				const p = result.data as { firstName: string; lastName: string } | undefined;
-				if (p) senderName = `${p.firstName} ${p.lastName}`;
+				const p = result.data as { displayName: string } | undefined;
+				if (p) senderName = p.displayName;
 			})
 		);
 	}
@@ -65,8 +65,8 @@ export async function load({ url, fetch, locals }) {
 					const code = (result.error as unknown as { code?: string })?.code;
 					throw error(result.response.status, getErrorMessage(code));
 				}
-				const p = result.data as { firstName: string; lastName: string } | undefined;
-				if (p) receiverName = `${p.firstName} ${p.lastName}`;
+				const p = result.data as { displayName: string } | undefined;
+				if (p) receiverName = p.displayName;
 			})
 		);
 	}

frontend/src/routes/briefwechsel/ConversationTimeline.svelte

@@ -10,8 +10,13 @@ interface Props {
 		documentDate?: string;
 		location?: string;
 		status: string;
-		sender?: { id: string; firstName: string; lastName: string } | null;
-		receivers?: { id: string; firstName: string; lastName: string }[];
+		sender?: {
+			id: string;
+			firstName?: string | null;
+			lastName: string;
+			displayName: string;
+		} | null;
+		receivers?: { id: string; firstName?: string | null; lastName: string; displayName: string }[];
 	}[];
 	senderId: string;
 	receiverId?: string;
@@ -67,9 +72,9 @@ function statusDotClass(status: string): string {
 function otherPartyName(doc: (typeof documents)[number]): string {
 	if (doc.sender?.id === senderId) {
 		const r = doc.receivers?.[0];
-		return r ? `${r.firstName} ${r.lastName}` : m.conv_no_party();
+		return r ? r.displayName : m.conv_no_party();
 	}
-	return doc.sender ? `${doc.sender.firstName} ${doc.sender.lastName}` : m.conv_no_party();
+	return doc.sender ? doc.sender.displayName : m.conv_no_party();
 }
 
 const newDocUrl = $derived(

frontend/src/routes/briefwechsel/CorrespondentSuggestionsDropdown.svelte

@@ -4,8 +4,9 @@ import { clickOutside } from '$lib/actions/clickOutside';
 
 interface Correspondent {
 	id: string;
-	firstName: string;
+	firstName?: string | null;
 	lastName: string;
+	displayName: string;
 }
 
 interface Props {
@@ -41,7 +42,9 @@ function handleKeydown(event: KeyboardEvent, container: HTMLElement) {
 }
 
 function getInitials(person: Correspondent): string {
-	return `${person.firstName.charAt(0)}${person.lastName.charAt(0)}`.toUpperCase();
+	if (person.firstName)
+		return `${person.firstName.charAt(0)}${person.lastName.charAt(0)}`.toUpperCase();
+	return person.lastName.substring(0, 2).toUpperCase();
 }
 </script>
 
@@ -78,7 +81,7 @@ function getInitials(person: Correspondent): string {
 					{getInitials(person)}
 				</span>
 				<!-- Svelte auto-escapes — do not use {@html} here. -->
-				{person.lastName}, {person.firstName}
+				{person.displayName}
 			</div>
 		{/each}
 	{/if}