dsh--flatten: A JSON Data Flattening Tool

`dsh--flatten` is an online tool plugin for DeepSeek Harness (DSH) that converts nested JSON data into a dot-separated flat key format. It supports bidirectional conversion and array index handling. Users can install it with `dsh plugin add dsh--flatten` and call the `flatten_` function in a session to transform data. Because it is a pure Node.js implementation, reviewing the source code before use is recommended.