G18 -- Never `git clean -x` where irreplaceable data is ignored-but-present

The dump, the memory images, the reverse-engineering database and the SDK live on the maintainer's disk under ignored paths; a -x clean deletes them. The backup is the text export of the database, the checksum files and a private archive repository — not the ignored directories. provenance: BFM R78 (the CLAUDE.md fail-safe since the rewrite)