dsh-useragent: Parsing User-Agent Strings to Identify Client Environments

The `dsh-useragent` plugin provided by DSH parses User-Agent strings to identify the browser, operating system, device type, engine, and crawler information. Maintained by uckkk, it is implemented in pure Node. Users can install it with `dsh plugin add dsh-useragent` and call the `parse_ua` tool during a session to perform parsing. It is suitable for scenarios that require determining the source of a request, but installing it executes third-party code, so its source code should be carefully reviewed for security.