test(geschichten): add drafts to the overview page test mock data

PR #813 made +page.svelte read data.drafts, which the load function
always returns, but the pre-existing page.svelte.test.ts mock predates
the field — all 15 tests crashed with TypeError on main after merge.

Closes #814
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

frontend/src/routes/geschichten/page.svelte.test.ts

@@ -31,6 +31,7 @@ const baseData = (overrides: Record<string, unknown> = {}) => ({
 	personFilters: [] as { id?: string; displayName: string }[],
 	documentFilter: null,
 	canBlogWrite: false,
+	drafts: [] as Array<{ id: string; title: string }>,
 	...overrides
 });