dsh-env-backup: DSH Environment Automatic Backup Plugin

dsh-env-backup is an automatic backup plugin for DSH environments, designed to resolve configuration confusion caused by plugin updates. It automatically backs up the `~/.dsh/profiles/web` directory when the plugin table changes, supporting rotating backup naming, retention policy configuration, and settings page integration. The plugin offers multiple trigger methods, supports automatic cleanup of old backups, and provides guidance for environment recovery. Users can install it via command and apply changes after a restart. Core features include automatic backup, precise cleanup that matches only specific backup names, and persistent configuration management. This plugin can effectively reduce the risk of losing environment configurations.