fix(journey): person chips rendered blank — share one PersonView→PersonOption projection

JourneyEditor fed GeschichteView.PersonView (no displayName) straight into
the displayName-rendering PersonMultiSelect, so every chip on a journey was
empty. The name mapping both editors need now lives once in
$lib/person/personOption.ts (with the [Unbekannt] fallback matching
GeschichteService.toView), and PersonMultiSelect/GeschichteSidebar import
the narrow PersonOption contract from there.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

frontend/src/lib/geschichte/GeschichteSidebar.svelte

@@ -1,10 +1,7 @@
 <script lang="ts">
 import { m } from '$lib/paraglide/messages.js';
-import type { components } from '$lib/generated/api';
 import PersonMultiSelect from '$lib/person/PersonMultiSelect.svelte';
-
-type Person = components['schemas']['Person'];
-type PersonOption = Pick<Person, 'id' | 'displayName'>;
+import type { PersonOption } from '$lib/person/personOption';
 
 interface Props {
 	status: 'DRAFT' | 'PUBLISHED';