dsh-crop-factor: DSH Equivalent Focal Length Conversion

The `dsh-crop-factor` plugin for DeepSeek Harness (DSH) is designed to meet the need for equivalent focal length conversion in photography agent development. Maintained by `uckkk`, it is implemented in pure Node.js, performs precise calculations, and has no network dependency. Users must install and enable it via a command, and it relies on specific versions of environment libraries. Since it runs with process privileges, reviewing the source code before installation is recommended. The plugin provides basic mathematical calculation capabilities for the DSH ecosystem and is suitable for vertical use cases such as photography assistance.