When the WiFi interface is down (e.g. USB adapter not activated),
scanning fails with "Network is down" errors. Now the scanner
proactively checks interface state via /sys/class/net and brings
it up using ip link (or ifconfig fallback) before attempting scans,
with a retry loop if the initial scan still fails.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>