dsh-study-plan: Exam Prep Time Allocation Tool

The core philosophy of DeepSeek Harness (DSH) is “everything is a plugin.” `dsh-study-plan` is an exam-preparation time allocation tool maintained by `uckkk`, implemented in pure Node.js for precise calculations without network dependency. The plugin registers the `study_plan` tool, enabling parameter-based calculations with detailed results, and is well suited for rapidly integrating exam-planning capabilities into the DSH ecosystem.