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/milestone.py

@@ -17,6 +17,7 @@ async def create(db: AsyncSession, study_id: uuid.UUID, milestone_in: MilestoneC
         actual_date=None,
         status=milestone_in.status or "NOT_STARTED",
         owner_id=milestone_in.owner_id,
+        site_id=milestone_in.site_id,
         notes=milestone_in.notes,
     )
     db.add(milestone)

backend/app/crud/site.py

@@ -46,3 +46,11 @@ async def list_by_study(db: AsyncSession, study_id: uuid.UUID, skip: int = 0, li
         select(Site).where(Site.study_id == study_id).offset(skip).limit(limit)
     )
     return result.scalars().all()
+
+
+async def get_sites_by_ids(db: AsyncSession, ids: set[uuid.UUID]) -> dict[uuid.UUID, Site]:
+    if not ids:
+        return {}
+    result = await db.execute(select(Site).where(Site.id.in_(ids)))
+    sites = result.scalars().all()
+    return {s.id: s for s in sites}

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)