feat: 书库导入导出/图片变体/书籍搜索/小组件运行时等

新增：
- 书库导入导出（library_import/library_export）及测试
- 图片变体生成（image_variants）与响应式图片（responsiveImage）
- 书籍搜索（bookSearch）+ BookSearch/LibrarySearchGrid 组件
- 小组件运行时（widgetRuntime）与静态检查（widgetLint）
- 上传缓存中间件（upload_cache）与字体 CSS 提取脚本

其它：
- 后端 handlers/services 全量调整
- 前端页面、组件、库函数与配置更新

backend/service/chat.go

@@ -75,8 +75,8 @@ type RoomView struct {
 	Joined      bool        `json:"joined"`
 	MyRole      string      `json:"my_role"`
 	UnreadCount int64       `json:"unread_count"`
-	Pinned      bool        `json:"pinned"`      // 对当前用户是否置顶（含大厅强制）
-	PinForced   bool        `json:"pin_forced"`  // 大厅强制置顶，不可取消
+	Pinned      bool        `json:"pinned"`         // 对当前用户是否置顶（含大厅强制）
+	PinForced   bool        `json:"pin_forced"`     // 大厅强制置顶，不可取消
 	Peer        *model.User `json:"peer,omitempty"` // 私聊对方（仅 direct）
 }
 
@@ -114,6 +114,15 @@ func (s *ChatService) membership(tx *gorm.DB, roomID, userID uint) (*model.ChatR
 	if err != nil {
 		return nil, err
 	}
+	// 过期禁言自动解除：惰性清理，不依赖定时任务
+	if m.Muted && m.MutedUntil != nil && m.MutedUntil.Before(time.Now()) {
+		m.Muted = false
+		m.MutedUntil = nil
+		_ = tx.Model(&model.ChatRoomMember{}).
+			Where("room_id = ? AND user_id = ?", roomID, userID).
+			Select("muted", "muted_until").
+			Updates(map[string]interface{}{"muted": false, "muted_until": nil}).Error
+	}
 	return &m, nil
 }
 
@@ -758,44 +767,85 @@ func (s *ChatService) Kick(operatorID, roomID, targetID uint, oversee bool) erro
 	return s.removeMember(roomID, targetID)
 }
 
-// SetMemberMute 禁言/解禁：群主、群管、全站监管；不可禁言群主或站点站长账号
-func (s *ChatService) SetMemberMute(operatorID, roomID, targetID uint, muted, oversee bool) error {
+// SendSystemMessage 向房间落库一条系统提示消息（sender_id=0，is_system=true），
+// 并推进房间 last_message_id 与 updated_at。失败返回 nil + error。
+func (s *ChatService) SendSystemMessage(roomID uint, content string) (*model.ChatMessage, error) {
+	msg := &model.ChatMessage{
+		RoomID:    roomID,
+		SenderID:  0,
+		Content:   content,
+		IsSystem:  true,
+		CreatedAt: time.Now(),
+	}
+	err := s.db.Transaction(func(tx *gorm.DB) error {
+		if err := tx.Create(msg).Error; err != nil {
+			return err
+		}
+		return tx.Model(&model.ChatRoom{}).Where("id = ?", roomID).
+			Updates(map[string]interface{}{
+				"last_message_id": msg.ID,
+				"updated_at":      time.Now(),
+			}).Error
+	})
+	if err != nil {
+		return nil, err
+	}
+	return msg, nil
+}
+
+// SetMemberMute 禁言/解禁：群主、群管、全站监管；不可禁言群主或站点站长账号。
+// duration 为禁言时长；0 表示永久禁言；muted=false 时忽略 duration 并清空 muted_until。
+// 返回目标用户昵称（供广播系统提示使用）。
+func (s *ChatService) SetMemberMute(operatorID, roomID, targetID uint, muted bool, duration time.Duration, oversee bool) (string, error) {
 	room, err := s.getRoom(roomID)
 	if err != nil {
-		return err
+		return "", err
 	}
 	if room.RoomType == model.ChatRoomTypeDirect {
-		return ErrChatOwnerOnly
+		return "", ErrChatOwnerOnly
 	}
 	target, err := s.membership(s.db, roomID, targetID)
 	if err != nil {
-		return err
+		return "", err
 	}
 	if target.Role == model.ChatRoleOwner {
-		return ErrChatCannotMuteOwner
+		return "", ErrChatCannotMuteOwner
 	}
 	var targetUser model.User
-	if err := s.db.Select("role").First(&targetUser, targetID).Error; err != nil {
-		return ErrChatUserGone
+	if err := s.db.Select("role", "nickname", "username").First(&targetUser, targetID).Error; err != nil {
+		return "", ErrChatUserGone
 	}
 	if targetUser.Role == model.RoleOwner {
-		return ErrChatCannotMuteOwner
+		return "", ErrChatCannotMuteOwner
 	}
 	if !oversee {
 		op, err := s.membership(s.db, roomID, operatorID)
 		if err != nil {
-			return err
+			return "", err
 		}
 		if op.Role != model.ChatRoleOwner && op.Role != model.ChatRoleAdmin {
-			return ErrChatMuteDenied
+			return "", ErrChatMuteDenied
 		}
 		if target.Role == model.ChatRoleAdmin && op.Role != model.ChatRoleOwner {
-			return ErrChatMuteDenied
+			return "", ErrChatMuteDenied
 		}
 	}
-	return s.db.Model(&model.ChatRoomMember{}).
+	var mutedUntil *time.Time
+	if muted && duration > 0 {
+		t := time.Now().Add(duration)
+		mutedUntil = &t
+	}
+	if err := s.db.Model(&model.ChatRoomMember{}).
 		Where("room_id = ? AND user_id = ?", roomID, targetID).
-		Select("muted").Update("muted", muted).Error
+		Select("muted", "muted_until").
+		Updates(map[string]interface{}{"muted": muted, "muted_until": mutedUntil}).Error; err != nil {
+		return "", err
+	}
+	targetName := targetUser.Nickname
+	if targetName == "" {
+		targetName = targetUser.Username
+	}
+	return targetName, nil
 }
 
 // SetMemberRole 仅站点站长可任命/撤销群管理员（admin <-> member）；不可改群主