headless-: CI Structured Output Plugin for DeepSeek Harness

`headless-` is a plugin designed for DeepSeek Harness (dsh) to enhance the reporting capabilities of CI pipelines. By subscribing to the session event stream, it transforms interactions into structured data and provides features such as JSON/NDJSON transaction reports, JUnit XML test reports, semantic exit codes, and file artifact collection. The plugin supports privacy masking, ensures deterministic output without interfering with standard output, and is suitable for automated evaluation scenarios in agent development.