dsh-lean: DeepSeek Session Cost Auditing and Tool Mode Monitoring

`dsh-lean` is a user-maintained client plugin designed to address the cost accounting challenges caused by DeepSeek Harness (DSH) peak-hour billing. It provides auditing functionality for session spend, off-peak costs, and tool mode consumption, retrieves detailed data via the command-line interface with `npx dsh-lean audit`, and helps developers achieve fine-grained cost control.