dsh-trash: DeepSeek Harness Trash Plugin

The DeepSeek Harness plugin dsh-trash provides accidental-deletion protection for agents by intercepting deletion commands such as `Remove-Item` and `rm` and converting them into operations that move files to `$DSH_HOME/trash`. It supports tools such as pwsh and bash, and provides trash listing, restore, and permanent deletion (`trash-purge`) capabilities. The plugin features cross-volume support, zero dependencies, and a fail-safe strategy to ensure data safety.