dsh-concurrency: Concurrency Requirement Estimation Plugin

DeepSeek Harness (DSH) introduces a workflow plugin called `dsh-concurrency`, designed to help users accurately estimate the concurrency requirements of agent development based on parameters, thereby effectively controlling costs and ensuring performance. The plugin is maintained by uckkk, implemented in pure Node, and has no network dependencies. Users can install it with the command `dsh plugin add github:uckkk/dsh-concurrency`, and after installation, they can invoke its tools in a session to obtain detailed results.