dsh-plugin-prune: DeepSeek Harness Plugin Usage Statistics and Cleanup

`dsh-plugin-prune` is a DeepSeek Harness plugin developed by Octo-o-o-o, designed to address the management challenges caused by accumulated “dead plugins.” The plugin operates in a purely observational mode and does not modify business state. It collects real-world tool invocation data, such as call counts, error rates, and latency, and provides a visualized health report in the “Plugin Health” tab of the Web interface. Users can use this information to score plugins and clean up unused ones. The data is persisted locally only and requires use with a specific version environment.