Fixed
- DNB add-by-ISBN no longer fails for German books with no OpenLibrary coverage (#608) — DNB results now carry a stable author ForeignID (GND from MARC 100 $0 when present, otherwise a synthetic
dnb:author:<name-slug>). When a canonical author (OpenLibrary / Hardcover) later arrives for the same SortName, the synthetic DNB row is migrated in place so the user keeps a single author record. Previously the add flow returned 422 "Author metadata unavailable" whenever no canonical provider had the ISBN.