dsh-baseboard: Baseboard Usage Calculator Plugin

The `dsh-baseboard` plugin launched by DeepSeek Harness (DSH) is designed to address baseboard material quantity calculation in agent workflows. Maintained by uckkk and implemented in pure Node.js, it operates without network dependencies and returns detailed calculation results directly. Users can install it with the `dsh plugin add` command and invoke its `baseboard` tool within a session. The plugin requires an execution environment that meets the version constraints of `@deepseek-ai/cordis` (`^4.0.1`) and `@deepseek-ai/dsh-tools` (`>=0.1.0-rc.6`).