f36a2b6059
前端未填 publisher_id 时传空字符串违反 tasks_ibfk_3(publisher_id→users.id)外键, 与 category_id 同类问题。将可空关联字段(publisher_id/publisher_org_id/claimed_by/ assign_park_id/assign_opc_id/park_id/category_id 及可空时间字段)统一清洗为 NULL; NOT NULL 列(deadline/published_at 等)保留空串原样,避免 1048