dsh-compact-and-branch: Convert Compressed Context into an Independent Branch Session

`dsh-compact-and-branch` is a standalone plugin for DeepSeek Harness, designed to provide clear session branch points. It reuses the built-in `/compact` logic to compress history, then creates a new root session that inherits the model configuration and full context, while the original session remains recoverable. Installation and use require enabling it via the command line and restarting DSH. It is well suited for scenarios with limited context windows, helping developers manage long-running projects.