feat(dns): 'hosts' output + /etc/hosts simulation docs

dns-records.sh <mode> hosts prints a marker-wrapped /etc/hosts block to pipe
into /etc/hosts (single-machine testing without a DNS server). README documents
apply/remove + the airgap caveat (spoof hosts break real internet while present).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tooling/dns-records.sh

@@ -40,9 +40,21 @@ names=("${services[@]}")
 case "$mode" in
   online) ;;
   airgap) names+=("${spoof[@]}") ;;
-  *) echo "usage: $0 [online|airgap]" >&2; exit 1 ;;
+  *) echo "usage: $0 [online|airgap] [hosts]" >&2; exit 1 ;;
 esac
 
+# Marker so /etc/hosts edits can be applied/removed cleanly.
+MARK="ulicraft ${mode}"
+
+# `hosts` format: print ONLY the /etc/hosts block (marker-wrapped) so it can be
+# piped straight into /etc/hosts to simulate the party DNS. See README.
+if [ "${2:-}" = hosts ]; then
+  echo "# >>> ${MARK} >>>"
+  for n in "${names[@]}"; do printf '%s %s\n' "$HOST_LAN_IP" "$n"; done
+  echo "# <<< ${MARK} <<<"
+  exit 0
+fi
+
 echo "# DNS records for mode=${mode}  ->  ${HOST_LAN_IP}"
 echo "# Configure these on your party DNS server (all A records to the host)."
 echo