dsh-turn-scratch: DSH Temp File Isolation and Cleanup Plugin

`dsh-turn-scratch` is a plugin designed specifically for DSH to manage temporary files generated in each conversation turn. It keeps the workspace clean through isolated storage, safe cross-drive transfer, and a staging area mechanism, and by default uses an “isolate before deleting” safety strategy to prevent accidental deletion. Users can adjust the storage path via configuration and use a set of commands to check status, restore, or clean up files. This plugin requires DSH version 0.1.1-rc.2 or later.