nuc: document LAN gateway migration 192.168.0.1 -> 192.168.0.2

Update host NIC/interfaces (gw + DNS to public 1.1.1.1/9.9.9.9, no
container dependency), fix transmission-bt kill-switch routes, and add a
note that DHCP instances self-heal while static ones (privoxy,
transmission-bt) must be updated by hand. Also spell out the macvlan
test-from-inside/external-host rule.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

nuc/transmission-bt.md

@@ -57,17 +57,17 @@ network:
         addresses: [192.168.0.254]
       routes:
         - to: 193.70.35.17/32
-          via: 192.168.0.1
+          via: 192.168.0.2
 EOF
 chmod 600 /etc/netplan/10-lxc.yaml
 netplan apply'
 
 # packages need a temporary default route (removed right after)
-incus exec "$CNAME" -- ip route add default via 192.168.0.1
+incus exec "$CNAME" -- ip route add default via 192.168.0.2
 incus exec "$CNAME" -- apt-get update
 incus exec "$CNAME" -- apt-get install -y --no-install-recommends \
     transmission-daemon wireguard-tools iptables curl
-incus exec "$CNAME" -- ip route del default via 192.168.0.1
+incus exec "$CNAME" -- ip route del default via 192.168.0.2
 
 # WireGuard full tunnel (generate key, print pubkey for the ks4 side)
 incus exec "$CNAME" -- bash -c 'umask 077