修复前后端显示异常问题（受试者、中心、负责人、日期等）

backend/app/crud/user.py

@@ -73,6 +73,14 @@ async def ensure_admin_exists(db: AsyncSession, *, default_password: str = "admi
     await db.commit()
 
 
+async def get_users_by_ids(db: AsyncSession, ids: set[uuid.UUID]) -> dict[uuid.UUID, User]:
+    if not ids:
+        return {}
+    result = await db.execute(select(User).where(User.id.in_(ids)))
+    users = result.scalars().all()
+    return {u.id: u for u in users}
+
+
 async def delete_user(db: AsyncSession, user: User) -> None:
     await db.execute(delete(StudyMember).where(StudyMember.user_id == user.id))
     await db.delete(user)