v1.0.0-rc1

docs(operations): document supported platforms for the .deb

Record the .deb supported-OS range (previously undocumented): currently
in-standard-support Debian/Ubuntu only — Ubuntu 22.04 + 24.04 LTS, Debian 12 +
13 — on amd64/arm64, systemd required, adduser required (now declared). Note the
binaries are statically linked (CGO_ENABLED=0) so the build/CI host OS does not
constrain where they run, that EOL releases (Ubuntu 20.04, Debian 11) are out of
the matrix, and that macOS is a separate manual install. Each release was
verified by a container apt-install + systemd-analyze verify.