dsh--csv: CSV ↔ JSON Conversion

DeepSeek Harness (DSH) provides the `dsh--csv` plugin to address the need for agents to convert data between JSON and CSV formats. Maintained by uckkk, it supports bidirectional conversion between arrays of JSON objects and CSV format, with header handling and quote escaping, and is implemented using pure Node.js. Users can install it with `dsh plugin add dsh--csv` and export JSON data to CSV using the `_to_csv` function. As the plugin includes third-party code, users are advised to review the source code themselves.