Introducing the dsh-practice-plan Plugin

dsh-practice-plan is a pure Node-based plugin for DeepSeek Harness (DSH) that generates instrument practice plans. It has no network dependencies and requires installing @deepseek-ai/cordis and @deepseek-ai/dsh-tools. Install it with `dsh plugin add github:uckkk/dsh-practice-plan`, after which the `practice_plan` tool can be invoked during a session.