feat(frontend): update generated API types and Geschichte routes for JourneyItem model

- api.ts: add GeschichteType, JourneyItem, GeschichteSummary schemas;
  remove documentId param from list endpoint; change list response to
  GeschichteSummary[]; add type + items to Geschichte; remove documents field
- GeschichteEditor: remove DocumentMultiSelect + documentIds from payload
  (journey items are managed via the future Lesereisen editor, not here)
- GET /geschichten page: remove documentId filter from server load + URL logic
- geschichten/new: remove documentId pre-population from server load
- geschichten/[id]: replace g.documents with g.items (document-backed JourneyItems)
- geschichten/new + [id]/edit: remove documentIds from submit payload type

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/routes/geschichten/+page.svelte

@@ -11,12 +11,11 @@ let { data }: { data: PageData } = $props();
 let showPersonPicker = $state(false);
 
 const selectedPersonIds = $derived(data.personFilters.map((p) => p.id!));
-const hasFilters = $derived(data.personFilters.length > 0 || !!data.documentFilter);
+const hasFilters = $derived(data.personFilters.length > 0);
 
 function rebuildUrl(personIds: string[]) {
 	const url = new URL(window.location.href);
 	url.searchParams.delete('personId');
-	url.searchParams.delete('documentId');
 	for (const id of personIds) url.searchParams.append('personId', id);
 	return url.pathname + url.search;
 }