fix(journey-editor): send {"note":null} on clear instead of omitting key

null ?? undefined evaluated to undefined, causing JSON.stringify to omit
the key entirely — the backend treated an absent note field as a no-op,
so clearing a note never persisted.

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

frontend/src/lib/geschichte/JourneyEditor.svelte

@@ -43,6 +43,7 @@ let items: JourneyItemView[] = $state(
 let titleTouched = $state(false);
 let mutationError = $state('');
 let liveAnnounce = $state('');
+let announceTimer: ReturnType<typeof setTimeout> | null = null;
 
 const titleEmpty = $derived(title.trim().length === 0);
 const showTitleError = $derived(titleEmpty && titleTouched);
@@ -138,7 +139,7 @@ async function handleNotePatch(itemId: string, note: string | null) {
 	const res = await csrfFetch(`/api/geschichten/${geschichte.id}/items/${itemId}`, {
 		method: 'PATCH',
 		headers: { 'Content-Type': 'application/json' },
-		body: JSON.stringify({ note: note ?? undefined })
+		body: JSON.stringify({ note: note })
 	});
 	if (!res.ok) throw new Error('note patch failed');
 	const updated: JourneyItemView = await res.json();
@@ -156,8 +157,10 @@ async function handleMoveUp(index: number) {
 	});
 	await handleReorder(ids);
 	// Clear so the live region does not re-announce on unrelated DOM mutations
-	setTimeout(() => {
+	if (announceTimer) clearTimeout(announceTimer);
+	announceTimer = setTimeout(() => {
 		liveAnnounce = '';
+		announceTimer = null;
 	}, 500);
 }
 
@@ -172,8 +175,10 @@ async function handleMoveDown(index: number) {
 	});
 	await handleReorder(ids);
 	// Clear so the live region does not re-announce on unrelated DOM mutations
-	setTimeout(() => {
+	if (announceTimer) clearTimeout(announceTimer);
+	announceTimer = setTimeout(() => {
 		liveAnnounce = '';
+		announceTimer = null;
 	}, 500);
 }