Query vpn_status (connected=0/1) alongside ping data. If VPN tunnel
is reported disconnected, gateway is immediately marked dead without
waiting for ping loss to accumulate. VPN status is checked with 1m
window (vs 3m for ping) since it updates every 10s.

Shows vpn=DOWN marker in --show output for affected gateways.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>