New decnet/rpki/ module mirrors decnet/asn/ shape. Validator ABC, lazy singleton factory (DECNET_RPKI_PROVIDER=ripestat default), paths.py with DECNET_RPKI_ROOT override. RipeStatValidator stub returns 'unknown' unconditionally — HTTP wired in next commit. enrich_rpki(ip, asn) -> (status, source) | (None, None); short-circuits on DECNET_RPKI_ENABLED=false or asn=None.