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]/+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
 				});
 		}