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/conversations/+page.server.ts

@@ -39,8 +39,8 @@ export async function load({ url, fetch }) {
 	if (senderId) {
 		requests.push(
 			api.GET('/api/persons/{id}', { params: { path: { id: senderId } } }).then(({ data }) => {
-				const p = data as { firstName: string; lastName: string } | undefined;
-				if (p) senderName = `${p.firstName} ${p.lastName}`;
+				const p = data as { displayName: string } | undefined;
+				if (p) senderName = p.displayName;
 			})
 		);
 	}
@@ -48,8 +48,8 @@ export async function load({ url, fetch }) {
 	if (receiverId) {
 		requests.push(
 			api.GET('/api/persons/{id}', { params: { path: { id: receiverId } } }).then(({ data }) => {
-				const p = data as { firstName: string; lastName: string } | undefined;
-				if (p) receiverName = `${p.firstName} ${p.lastName}`;
+				const p = data as { displayName: string } | undefined;
+				if (p) receiverName = p.displayName;
 			})
 		);
 	}