Asynchronously creates one or more BDMS.Models.Stratigraphy entries, each together with the contents of one of its tabs (currently only the Lithology tab is implemented). Used both by the "add stratigraphy" action (a single header-only edit) and by the extraction modal that bulk-adds 1–n stratigraphies with their lithology contents. All edits must target the same borehole; a duplicate name (already on the borehole or repeated within the batch) is rejected with a `mustBeUnique` error.