Evicting or deleting a local RPM removed the local_files row but left its
rpm_metadata behind, so generated repodata kept listing a package that no
longer exists. Deletes now run a provider cleanup hook symmetric to the
existing upload hook.
- add PostDeleteHook and MetadataDeleter provider interfaces, plus a
DeleteRPMMetadata DB method
- implement AfterDelete in the RPM provider to drop the metadata row
- route both local delete paths (evictLocal and the files handler) through
a shared deleteLocalFile helper that removes the file then runs the hook
- cover the cleanup with a dockerised test
