On hosts where the kernel has IPv6 disabled, binding `::1` fails with
EAFNOSUPPORT rather than EADDRNOTAVAIL. canListenOnHost treated that as
"port taken", so `vp run dev` reported every port from 0 to 65535 as
unavailable and findAvailablePort never returned the preferred port.
Treat EAFNOSUPPORT the same as EADDRNOTAVAIL.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CxLHnfmdqBAuYjahhhM2jo