修复前后端显示异常问题（受试者、中心、负责人、日期等）

backend/app/api/v1/tasks.py

@@ -8,7 +8,9 @@ from app.crud import audit as audit_crud
 from app.crud import milestone as milestone_crud
 from app.crud import study as study_crud
 from app.crud import task as task_crud
+from app.crud import user as user_crud
 from app.schemas.task import TaskCreate, TaskRead, TaskUpdate
+from app.schemas.user import UserDisplay
 
 router = APIRouter()
 
@@ -47,6 +49,9 @@ async def create_task(
     await _ensure_study_exists(db, study_id)
     await _validate_milestone(db, study_id, task_in.milestone_id)
     task = await task_crud.create(db, study_id, task_in, created_by=current_user.id)
+    assignee = None
+    if task.assignee_id:
+        assignee = await user_crud.get_by_id(db, task.assignee_id)
     await audit_crud.log_action(
         db,
         study_id=study_id,
@@ -57,7 +62,7 @@ async def create_task(
         operator_id=current_user.id,
         operator_role=current_user.role,
     )
-    return task
+    return _to_task_read(task, assignee)
 
 
 @router.get(
@@ -74,7 +79,13 @@ async def list_tasks(
 ) -> list[TaskRead]:
     await _ensure_study_exists(db, study_id)
     tasks = await task_crud.list_tasks(db, study_id, milestone_id=milestone_id, assignee_id=assignee_id, status=status)
-    return list(tasks)
+    assignee_ids = {t.assignee_id for t in tasks if t.assignee_id}
+    users_map = await user_crud.get_users_by_ids(db, assignee_ids)
+    result: list[TaskRead] = []
+    for t in tasks:
+        user = users_map.get(t.assignee_id)
+        result.append(_to_task_read(t, user))
+    return result
 
 
 @router.patch(
@@ -98,6 +109,9 @@ async def update_task(
 
     old_status = task.status
     updated = await task_crud.update(db, task, task_in)
+    assignee = None
+    if updated.assignee_id:
+        assignee = await user_crud.get_by_id(db, updated.assignee_id)
     detail = None
     if task_in.status and task_in.status != old_status:
         detail = f"task {task_id} status {old_status} -> {task_in.status}"
@@ -111,4 +125,23 @@ async def update_task(
         operator_id=current_user.id,
         operator_role=current_user.role,
     )
-    return updated
+    return _to_task_read(updated, assignee)
+
+
+def _to_task_read(task, assignee) -> TaskRead:
+    return TaskRead(
+        id=task.id,
+        study_id=task.study_id,
+        milestone_id=task.milestone_id,
+        title=task.title,
+        description=task.description,
+        assignee_id=task.assignee_id,
+        assignee=UserDisplay.model_validate(assignee) if assignee else None,
+        priority=task.priority,
+        due_date=task.due_date,
+        status=task.status,
+        completed_at=task.completed_at,
+        created_by=task.created_by,
+        created_at=task.created_at,
+        updated_at=task.updated_at,
+    )