[Server] 다른 유저 정보 가져오기

# ISSUE
- Group: client, server, sr (선택해주세요)
- Type: bug, feature, delete (선택해주세요)
- Detail: '커밋 메시지 형식으로 작성해주세요'
-
# TODO

- [ ] Job1
- [ ] Job2
- [ ] Job3

# Estimated time
> Pick one (작업 시간 선택)

`0.5h`
`1h`
`1.5h`
`2h`
`2.5h`
`3h`

# Labels
(우측 사이드바에서 라벨을 선택해주세요)
- Estimated time: `E: 1h`
- Group : `client`, `server`
- Sprint: `Sprint__NUMBER__`
- Urgency: `High`, `Middle`, `Low`

No files, tests, entry points, or concrete acceptance criteria are named. First clarify which other-user information the server should expose, the relevant endpoint and authorization rules, and how completion will be verified. The issue is done only when those requirements and tests are defined and implemented.

Written by the indexing model from the issue text.