Switch NetworkManager WiFi backend to iwd to resolve repeated
wpa_supplicant disconnects caused by nl80211 send_event_marker
incompatibility with iwlwifi. Each disconnect was triggering avahi
SIGHUP reloads, causing .local name resolution to fail for several
minutes at a time.
Also disable WiFi power save in TLP and enable IPv6 mDNS resolution
via NSS (nssmdns6) for hosts that only advertise IPv6 addresses.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
