feat(conversations): add notification mute functionality for conversations

- Rename Muted field to NotificationMuted across model, DTOs and converters
- Add UpdateNotificationMuted repository method with upsert support
- Add SetConversationNotificationMuted service method
- Add PUT /:id/notification_muted route for setting mute status
- Improve S3 storage resilience by skipping bucket check on access denied

internal/service/chat_service.go

@@ -27,7 +27,8 @@ type ChatService interface {
 	GetConversationList(ctx context.Context, userID string, page, pageSize int) ([]*model.Conversation, int64, error)
 	GetConversationByID(ctx context.Context, conversationID string, userID string) (*model.Conversation, error)
 	DeleteConversationForSelf(ctx context.Context, conversationID string, userID string) error
-	SetConversationPinned(ctx context.Context, conversationID string, userID string, isPinned bool) error
+SetConversationPinned(ctx context.Context, conversationID string, userID string, isPinned bool) error
+	SetConversationNotificationMuted(ctx context.Context, conversationID string, userID string, notificationMuted bool) error
 
 	// 消息操作
 	SendMessage(ctx context.Context, senderID string, conversationID string, segments model.MessageSegments, replyToID *string) (*model.Message, error)
@@ -215,6 +216,32 @@ func (s *chatServiceImpl) SetConversationPinned(ctx context.Context, conversatio
 	return nil
 }
 
+// SetConversationNotificationMuted 设置会话免打扰状态（用户维度）
+func (s *chatServiceImpl) SetConversationNotificationMuted(ctx context.Context, conversationID string, userID string, notificationMuted bool) error {
+	participant, err := s.getParticipant(ctx, conversationID, userID)
+	if err != nil {
+		if errors.Is(err, gorm.ErrRecordNotFound) {
+			return errors.New("conversation not found or no permission")
+		}
+		return fmt.Errorf("failed to get participant: %w", err)
+	}
+	if participant.ConversationID == "" {
+		return errors.New("conversation not found or no permission")
+	}
+
+	if err := s.repo.UpdateNotificationMuted(conversationID, userID, notificationMuted); err != nil {
+		return fmt.Errorf("failed to update notification_muted status: %w", err)
+	}
+
+	// 失效缓存
+	if s.conversationCache != nil {
+		s.conversationCache.InvalidateParticipant(conversationID, userID)
+		s.conversationCache.InvalidateConversationList(userID)
+	}
+
+	return nil
+}
+
 // SendMessage 发送消息（使用 segments）
 func (s *chatServiceImpl) SendMessage(ctx context.Context, senderID string, conversationID string, segments model.MessageSegments, replyToID *string) (*model.Message, error) {
 	// 首先验证会话是否存在