chii_crt_subject_index 缺少是否剧透字段

目前条目-角色关联可勾选是否剧透，schema 中暂无此字段

Locate the schema definition for chii_crt_subject_index and inspect how the item-character association stores the existing spoiler choice. Add the missing schema field with the project’s established type and naming conventions, then verify that the association can persist and retrieve the checkbox value. Done means the schema represents the spoiler field without breaking existing records.

Written by the indexing model from the issue text.