Upstream installer.sh always runs `netbird service stop` and
`netbird service uninstall` with stderr shown. uninstall_preflight_steps
has already removed the service by then, so every upgrade printed two
launchctl errors even though nothing failed.
Run the same steps from postflight_steps instead and silence only the
stop and uninstall calls. A failed service install or start now fails
the cask instead of being swallowed by `|| true`.
tri