refactor(geschichte): extract delete handler to [id]/+page.svelte, pass via ondelete prop

Moves the confirm-then-delete flow out of StoryReader and JourneyReader into
the single [id]/+page.svelte owner. Both reader components gain an optional
ondelete prop — the delete button calls ondelete?.() so the handler is opt-in
and never duplicated. Tests verify the prop is called on click.

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

frontend/src/lib/geschichte/JourneyReader.svelte

@@ -1,8 +1,5 @@
 <script lang="ts">
 import { m } from '$lib/paraglide/messages.js';
-import { goto } from '$app/navigation';
-import { getConfirmService } from '$lib/shared/services/confirm.svelte';
-import { csrfFetch } from '$lib/shared/cookies';
 import JourneyItemCard from './JourneyItemCard.svelte';
 import JourneyInterlude from './JourneyInterlude.svelte';
 import type { components } from '$lib/generated/api';
@@ -13,9 +10,10 @@ type JourneyItemView = components['schemas']['JourneyItemView'];
 interface Props {
 	geschichte: GeschichteView;
 	canBlogWrite: boolean;
+	ondelete?: () => Promise<void>;
 }
 
-let { geschichte: g, canBlogWrite }: Props = $props();
+let { geschichte: g, canBlogWrite, ondelete }: Props = $props();
 
 // Render intro only when body is a non-empty, non-whitespace string.
 const introText = $derived(g.body?.trim() ? g.body : null);
@@ -27,23 +25,6 @@ const validItems = $derived(
 			item.document != null || (item.note != null && item.note.trim().length > 0)
 	)
 );
-
-const confirm = getConfirmService();
-
-async function handleDelete() {
-	const ok = await confirm.confirm({
-		title: m.geschichte_delete_confirm_title(),
-		body: m.geschichte_delete_confirm_body(),
-		confirmLabel: m.btn_delete(),
-		cancelLabel: m.btn_cancel(),
-		destructive: true
-	});
-	if (!ok) return;
-	const res = await csrfFetch(`/api/geschichten/${g.id}`, { method: 'DELETE' });
-	if (res.ok) {
-		goto('/geschichten');
-	}
-}
 </script>
 
 {#if introText}
@@ -80,7 +61,7 @@ async function handleDelete() {
 		</a>
 		<button
 			type="button"
-			onclick={handleDelete}
+			onclick={() => ondelete?.()}
 			class="inline-flex h-11 items-center rounded font-sans text-sm font-medium text-danger hover:underline focus:outline-none focus-visible:ring-2 focus-visible:ring-focus-ring"
 		>
 			{m.btn_delete()}