dsh-chat-tree: Conversation Branch Visualization Plugin

`dsh-chat-tree` is a DeepSeek Harness plugin designed to address the inconvenience of viewing multi-branch conversations. It visualizes conversation branches with an interactive tree diagram, supporting quick navigation, sidebar collapsing, and node detail cards (such as renaming and changing colors). The plugin supports branch operations, including continuing conversations, bookmarking, splitting/merging, and deletion (first turn only). Users can customize the visible tree scope, node size, and styling. It depends on `schemastery` and requires DSH version `>=0.1.5-rc.2`. This tool is suitable for users who need to efficiently manage multi-branch conversations.