dsh-turnsnap: Zero-Config Per-Turn Git Checkpoints for DeepSeek Harness

The `dsh-turnsnap` plugin for DeepSeek Harness (DSH) automatically creates rollback-capable checkpoints for a Git working directory by monitoring agent turn events, addressing the problem of uncontrollable state in long sessions. It is ready to use after installation and requires no configuration. At the end of each turn, it automatically runs `git add -A` and commits, using a serialized queue to prevent concurrent conflicts. The plugin provides tools for pausing, resuming, and checking status, and can be controlled through natural language or scripts. Note that staged changes are merged, and checkpoint commits skip Pre-commit Hooks.