relay: bind the host LAN IP, admit the podman bridge subnet only

169.254.1.2 is not a local address on this host (netavark runs its
bridges in aardvark-dns' netns), so the relay cannot bind it — and a
loopback bind refuses container traffic. Probe-socket proof: a host
socket on 192.168.0.143:18094 answers the container's 169.254.1.2:18094
dial while the LAN IP refuses from the container. The relay binds
192.168.0.143:18093 and the deployer installs an iptables INPUT pair
(ACCEPT 10.89.0.0/16, DROP rest) so the unauthenticated endpoint stays
off the LAN.

shared/prometheus/alertmanager.yml

@@ -2,8 +2,9 @@
 # Deployed to /opt/alertmanager/config/alertmanager.yml on Dankclaw.
 #
 # The one delivery path is Signal. The webhook lands on the host-side
-# signal-relay (a systemd user unit listening on 169.254.1.2:18093, the
-# host.containers.internal endpoint), which
+# signal-relay (a systemd user unit listening on 192.168.0.143:18093, the
+# host LAN IP — the address the container's host.containers.internal dial
+# lands on), which
 # formats the group and hands it to signal-cli under Frank's existing
 # account. There is deliberately no second receiver: a duplicate channel is
 # how an alert starts arriving twice and getting muted everywhere.