dsh-backup-plan: Backup Policy

`dsh-backup-plan` is a backup policy management plugin for DeepSeek Harness (DSH), maintained by uckkk. It is designed to address cases where generic solutions cannot meet specific backup requirements, providing precise calculations based on parameters and clear recommendations. The plugin is implemented purely in Node and has no network dependencies. Its source code and environment dependencies should be reviewed before installation. It runs with the permissions of the current process, and its tools can be invoked directly within DSH sessions after installation.