Export a project's grading rubric to YAML
rubric_export.RdWrites the rubric stored in the project's grading database (each question's
rubric items, in display order, plus its scoring setup when one has been
configured) to a YAML file. The file contains no per-repository grading
data, so it can be shared, edited by hand or by an LLM tool, and brought
back with rubric_import(). The file format is described by the JSON
Schema at system.file("schema/markermd-rubric.json", package = "markermd").