`hostname -I` is GNU-only and errors on BSD/macOS, so when the public-IP
curl couldn't reach api.ipify.org the script printed nothing and the
tmux status bar showed an empty IP. Try `ipconfig getifaddr` for common
interfaces first, fall back to `hostname -I` on Linux, then `ifconfig`
as a last resort. Also guard against empty-but-zero-exit curl output.
The DigitalOcean metadata endpoint for reserved/floating IPv4 is
/metadata/v1/{reserved,floating}_ip/ipv4/ip_address, not .../address.
The .../active check works but the wrong IP path returned an empty
body, causing the script to silently fall through to ipify on every
droplet with a reserved/floating IP attached.
Verified on a droplet:
curl .../reserved_ip/ipv4/ip_address -> 45.55.111.240
curl .../reserved_ip/ipv4/address -> (empty)
If /sys/class/dmi/id/sys_vendor says DigitalOcean and the droplet has
a reserved_ip or floating_ip assigned, use that over the ipify-based
egress IP. Keeps the ipify/hostname -I fallback intact for other hosts.
Gated on the DMI check so non-DO hosts skip the metadata probe entirely
and the tmux status bar refresh stays fast.
