feat(lesereisen): implement lesereisen

frontend/src/lib/person/personFormat.ts

@@ -1,4 +1,5 @@
 import { formatDate } from '$lib/shared/utils/date';
+import { m } from '$lib/paraglide/messages.js';
 
 type Person = { firstName?: string | null; lastName: string; displayName: string };
 type DocForMeta = {
@@ -17,6 +18,19 @@ function djb2(str: string): number {
 	return Math.abs(hash);
 }
 
+/** Localized fallback when a person has no name parts. */
+export function unknownPersonName(): string {
+	return m.person_unknown();
+}
+
+/**
+ * Single source for the join-names-or-fallback rule. Mirrors the server-side
+ * fallback in GeschichteService.toView (which emits the literal '[Unbekannt]').
+ */
+export function joinNameOrUnknown(firstName?: string | null, lastName?: string | null): string {
+	return [firstName, lastName].filter(Boolean).join(' ').trim() || unknownPersonName();
+}
+
 export function getInitials(name: string): string {
 	const words = name.trim().split(/\s+/).filter(Boolean);
 	if (words.length === 0) return '';