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.server.ts

@@ -9,15 +9,13 @@ type Person = components['schemas']['Person'];
 export const load: PageServerLoad = async ({ url, fetch }) => {
 	const api = createApiClient(fetch);
 	const personIds = url.searchParams.getAll('personId');
-	const documentId = url.searchParams.get('documentId') ?? undefined;
 
 	const [listResult, ...personResults] = await Promise.all([
 		api.GET('/api/geschichten', {
 			params: {
 				query: {
 					status: 'PUBLISHED',
-					personId: personIds.length ? personIds : undefined,
-					documentId
+					personId: personIds.length ? personIds : undefined
 				}
 			}
 		}),
@@ -34,7 +32,6 @@ export const load: PageServerLoad = async ({ url, fetch }) => {
 
 	return {
 		geschichten: listResult.data ?? [],
-		personFilters,
-		documentFilter: documentId ?? null
+		personFilters
 	};
 };