Allow -P to install from freebsd-base(7) pkgbase packages, which is
now the default. Setting NANO_NOPKGBASE falls back to the legacy
distribution sets. Document the behavior in nanobsd(8).
Run pkg(8) directly against NANO_WORLDDIR with explicit ABI
and OSVERSION overrides.
Install every pkg repo fingerprint from the source tree share/keys
directory instead of a single hardcoded fingerprint heredoc.
Co-authored-by: Jose Luis Duran <jlduran@FreeBSD.org>
Sponsored by: Google LLC (GSoC 2026)