chore(scripts/release): emit per-target tarballs alongside deb/rpm
Each triple now also gets leveva-<ver>-<triple>.tar.gz carrying the
same payload as the package asset tables in leveva/Cargo.toml (binary,
systemd unit, default config + MOTD, example config, license), for
platforms without dpkg/rpm. Collected into var/dist/ with the packages.
Assisted-by: Claude Fable 5 via Claude Code
Signed-off-by: Xe Iaso <me@xeiaso.net>