fix(lists): pass nextCompleted argument to api.toggleListItem and make parameter optional

frontend/src/lib/api.ts

@@ -487,7 +487,7 @@ export const api = {
     });
   },
 
-  async toggleListItem(listId: string, itemId: string, isCompleted: boolean): Promise<ListItem> {
+  async toggleListItem(listId: string, itemId: string, isCompleted?: boolean): Promise<ListItem> {
     return request<ListItem>(`/api/v1/lists/${listId}/items/${itemId}`, {
       method: 'PATCH',
       body: JSON.stringify({ isCompleted }),