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/routes/geschichten/[id]/+page.svelte

@@ -1,6 +1,10 @@
 <script lang="ts">
+import { goto } from '$app/navigation';
 import { m } from '$lib/paraglide/messages.js';
 import { formatDate } from '$lib/shared/utils/date';
+import { formatAuthorDisplayName } from '$lib/geschichte/utils';
+import { getConfirmService } from '$lib/shared/services/confirm.svelte';
+import { csrfFetch } from '$lib/shared/cookies';
 import BackButton from '$lib/shared/primitives/BackButton.svelte';
 import StoryReader from '$lib/geschichte/StoryReader.svelte';
 import JourneyReader from '$lib/geschichte/JourneyReader.svelte';
@@ -16,8 +20,23 @@ const publishedAt = $derived.by(() => {
 	return formatDate(g.publishedAt.slice(0, 10), 'long');
 });
 
-function authorName(): string {
-	return g.author?.displayName ?? '';
+const authorName = $derived(formatAuthorDisplayName(g.author));
+
+const confirm = getConfirmService();
+
+async function handleDelete() {
+	const ok = await confirm.confirm({
+		title: m.geschichte_delete_confirm_title(),
+		body: m.geschichte_delete_confirm_body(),
+		confirmLabel: m.btn_delete(),
+		cancelLabel: m.btn_cancel(),
+		destructive: true
+	});
+	if (!ok) return;
+	const res = await csrfFetch(`/api/geschichten/${g.id}`, { method: 'DELETE' });
+	if (res.ok) {
+		goto('/geschichten');
+	}
 }
 </script>
 
@@ -41,15 +60,15 @@ function authorName(): string {
 				{/if}
 			</div>
 			<p class="font-sans text-sm text-ink-3">
-				{authorName()}
+				{authorName}
 				{#if publishedAt}· {m.geschichten_published_on({ date: publishedAt })}{/if}
 			</p>
 		</header>
 
 		{#if isJourney}
-			<JourneyReader geschichte={g} canBlogWrite={data.canBlogWrite} />
+			<JourneyReader geschichte={g} canBlogWrite={data.canBlogWrite} ondelete={handleDelete} />
 		{:else}
-			<StoryReader geschichte={g} canBlogWrite={data.canBlogWrite} />
+			<StoryReader geschichte={g} canBlogWrite={data.canBlogWrite} ondelete={handleDelete} />
 		{/if}
 	</article>
 </div>