dsh-stddev: Standard Deviation Calculator

The **dsh-stddev** plugin for DeepSeek Harness (DSH) provides standard deviation calculation capabilities and is maintained by uckkk. Implemented in pure Node with no network dependencies, it is configured through `cordis.patch.yml`. It can be installed using the command `dsh plugin add github:uckkk/dsh-stddev`, after which its registered tool can be called directly. Licensed under the MIT License, the plugin depends on the DSH toolkit and adds basic statistical computation to the plugin ecosystem.