relay: admit loopback and the host itself before the DROP

The bridge-subnet-only pair dropped the host's own health probe
(source 192.168.0.143/127.0.0.1) and failed a healthy deploy. The
deployer now installs the full set: ACCEPT 127.0.0.1, ACCEPT the host
IP, ACCEPT 10.89.0.0/16, then DROP.

tests/observability_quadlet.bats

@@ -475,6 +475,8 @@ assert any('ALERTS' in e for e in exprs), exprs
     grep -q 'SIGNAL_CLI = "/usr/local/bin/signal-cli"' "$relay"
     grep -q 'SIGNAL_ACCOUNT = "318311"' "$relay"
     grep -q 'LISTEN_ADDR = ("192.168.0.143", 18093)' "$relay"
+    grep -q -- '--dport 18093 -s 127.0.0.1 -j ACCEPT' "$handler"
+    grep -q -- '--dport 18093 -s 192.168.0.143 -j ACCEPT' "$handler"
     grep -q -- '--dport 18093 -s 10.89.0.0/16 -j ACCEPT' "$handler"
     grep -q -- '--dport 18093 -j DROP' "$handler"
 }