### Summary
```
/api/v1/chats/<chat_id>/sessions/<session_id>/messages/<msg_id> DELETE
/api/v1/chats/<chat_id>/sessions/<session_id>/messages/<msg_id>/feedback PUT
```
Migrates the chat session message delete and feedback APIs to the Go
server, matching the Python behavior for authorization, session
ownership checks, message/reference updates, and feedback validation.