业务更名为撞车并切换crash路由

用户可见文案与页面/API路径改为撞车与crash，保留mohong表与权限码兼容；移动端入口去掉租/撞图标。

backend/internal/modules/chat/conversation.go

@@ -169,6 +169,22 @@ func (r *Repository) EnsureSupportConversation(ctx context.Context, userID uint6
 				_ = tx.Model(&existing).Update("support_scene", SupportSceneGeneral).Error
 			}
 		}
+		// 兼容旧摸大红场景码 mohong → crash
+		if existing.ID == 0 && scene == SupportSceneCrash {
+			err = tx.Table("chat_conversations AS c").
+				Select("c.*").
+				Joins("JOIN chat_participants AS cp ON cp.conversation_id = c.id").
+				Where(
+					"c.type = ? AND c.support_scene = ? AND cp.participant_type = ? AND cp.participant_id = ?",
+					ConversationTypeGeneralSupport, SupportSceneMohong, "user", userID,
+				).
+				Order("c.id ASC").
+				Limit(1).
+				Find(&existing).Error
+			if err != nil {
+				return err
+			}
+		}
 		if existing.ID > 0 {
 			conversationID = existing.ID
 			return nil