fix(message): add missing BatchDecryptMessagesParallel in GetLastMessagesBatch

GetLastMessagesBatch was returning empty segments because it skipped
the decryption step that all other message query methods perform.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

internal/repository/message_repo.go

@@ -933,12 +933,15 @@ func (r *messageRepository) GetLastMessagesBatch(ctx context.Context, convIDs []
 		return nil, err
 	}
 
+	if len(messages) > 0 {
+		model.BatchDecryptMessagesParallel(messages)
+	}
+
 	for _, m := range messages {
 		result[m.ConversationID] = m
 	}
 	return result, nil
 }
-
 // GetParticipantsBatch 批量获取多个会话的参与者列表
 func (r *messageRepository) GetParticipantsBatch(ctx context.Context, convIDs []string) (map[string][]*model.ConversationParticipant, error) {
 	result := make(map[string][]*model.ConversationParticipant, len(convIDs))