dsh-turn-fork: Turn-based editing, retrying, and version tree navigation for DeepSeek Harness sessions

`dsh-turn-fork` is an MIT-licensed plugin for DeepSeek Harness designed to address the issues of modifying historical user messages and rerunning. It supports editing confirmed messages and provides two downstream strategies: "truncate" or "keep," enabling the creation of a new branch from that turn and rerunning. Core features include retrying historical turns via per-turn buttons, regenerating assistant responses via message buttons or session headers, and providing a version tree Timeline for viewing branch summaries, navigation (Undo/Redo), and managing run status. Its branch logs are persistent and readable after process restarts, and it utilizes only official slots to avoid DOM injection. The installation command is `dsh plugin add dsh-turn-fork`, which requires a process restart to take effect. The plug...