完善角色与消息权限：收紧板管内容处置，彻底删除仅站长，并统一管理删帖/评弹窗。

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/service/post.go

@@ -15,7 +15,7 @@ import (
 var (
 	ErrPostNotFound     = errors.New("帖子不存在")
 	ErrPostForbidden    = errors.New("无权限操作此帖子")
-	ErrPostDeleteMeta   = errors.New("管理删除须填写类型与理由")
+	ErrPostDeleteMeta   = errors.New("选「其他」时须填写删除理由")
 	ErrPostInvalidType  = errors.New("无效的删除类型")
 )
 
@@ -1083,16 +1083,27 @@ func (s *PostService) Delete(actor *Actor, postID, userID uint, opts DeletePostO
 	if post.UserID == userID {
 		staffDeleted = false
 	} else if actor != nil && actor.CanModerateBoard(post.BoardID) {
+		var author model.User
+		if err := s.db.Select("role").First(&author, post.UserID).Error; err != nil {
+			return false, authorID, ErrPostNotFound
+		}
+		if !actor.CanModerateAuthor(author.Role) {
+			return false, authorID, ErrAuthorProtected
+		}
 		deleteType = strings.TrimSpace(opts.DeleteType)
 		deleteReason = strings.TrimSpace(opts.DeleteReason)
 		if !model.ValidPostDeleteType(deleteType) {
 			return false, authorID, ErrPostInvalidType
 		}
-		if deleteReason == "" {
-			return false, authorID, ErrPostDeleteMeta
-		}
-		if len([]rune(deleteReason)) > 200 {
-			return false, authorID, errors.New("删除理由不能超过 200 字")
+		if deleteType == model.PostDeleteTypeOther {
+			if deleteReason == "" {
+				return false, authorID, ErrPostDeleteMeta
+			}
+			if len([]rune(deleteReason)) > 200 {
+				return false, authorID, errors.New("删除理由不能超过 200 字")
+			}
+		} else {
+			deleteReason = ""
 		}
 		staffDeleted = true
 	} else {