Add hack/check-host-runtime.bats with six self-contained test cases that
exercise the check-host-runtime.sh preflight script: clean host exits
silently, standalone containerd.service warns, standalone docker.service
warns, both services warn, du failures do not suppress warnings, and the
socket-only fallback fires when systemctl is unavailable.
Tests inject a stub systemctl and du binary via PATH and redirect the
script's probe paths through COZYSTACK_PREFLIGHT_* environment variables,
so they run without root and on any host (including non-systemd macOS).
Assisted-By: Claude <noreply@anthropic.com>
Signed-off-by: Aleksei Sviridkin <f@lex.la>
55c2dcf869