dsh-wsl-cal: Read-Only Calendar Query Plugin for WSL

`dsh-wsl-cal` is a WSL plugin for DeepSeek Harness (DSH), designed to meet agents' need to read Linux calendar information. By integrating the `khal` tool, it provides read-only calendar query capabilities, including checking availability and retrieving schedules for today and the next N days. It enables agents to access the calendar through a standardized command-line interface, without creating or modifying events. Users can install it via the official command and must configure `khal` themselves.