POST /v0/users/-/collections/{subject_id} 修改收藏状态在时间线表现和网页修改不一致

如果不在 Request body 写上 comment，时间线会不展示 comment，但收藏还保留着 comment。按照网页操作逻辑，只修改状态应该在时间线显示 comment？
示例：https://bgm.tv/user/inchei/timeline （2025-6-14）

Start at the POST /v0/users/-/collections/{subject_id} endpoint and trace how the request body’s comment is handled when the collection status changes. Compare the API behavior with the linked timeline example from 2025-06-14 and verify whether an update without a comment should display the existing comment. Done means the timeline behavior matches the web operation consistently.

Written by the indexing model from the issue text.