dsh-snapshot: Adds file snapshot and undo to DeepSeek Harness

# Introduction Running agents in DeepSeek Harness (DSH) commonly involves using `write`/`edit` to modify files. Once these operations are executed, the original content of the file is overwritten. If the model makes a mistake or a batch refactor corrupts a critical file, the content prior to the change becomes unrecoverable, necessitating manual backups or version control for remediation. dsh-snapshot implements this as a plugin: it automatically backs up file history after every `write`/`edit` call, allowing for restoration to any previous version when needed. Below, we introduce its features, installation methods, and usage notes. # What is dsh-snapshot? dsh-snapshot is a host plugin for DeepSeek Harness maintained by Hyna-hla.