dsh-multi-user: DeepSeek Harness Single-Process Multi-User View Tiering Plugin

The dsh-multi-user plugin enables single-machine multi-user isolation for DeepSeek Harness through a JWT login wall, tiered views, and user management features. Users can join specific workspace paths and view only authorized content. The plugin requires no extra gateway, is easy to install, and is suitable for lightweight multi-user tiered-view scenarios. Note that its security boundary is limited: agent tools within the same process can still operate on arbitrary host paths.