dsh-fork-graph: Display session forking topology in DSH session header

`dsh-fork-graph` is a Web plugin for DeepSeek Harness (DSH) maintained by chouyong and released under the MIT License. Its core functionality is to transform DSH session fork relationships from a traditional flat list into a git-graph style visual topology graph. Rather than replacing DSH's fork action or maintaining independent data, the plugin performs a pure projection of existing session list data. It aims to clearly visualize the lineage of "which session forked from which session" and supports clicking to jump between branch nodes. Key features include displaying colored branch lanes and fork curves in the session header, showing the title and status (e.g., current, running) for each node, and defaulting focus to the current session's line.