docker: make healthcheck separate

docker/healthcheck.sh

@@ -0,0 +1,16 @@
+#!/bin/bash
+# returns 0 when chatmail-init succeeded and all expected services are running.
+
+set -e
+
+test -f /run/chatmail-init.done
+
+# Core services
+services="chatmail-metadata doveauth dovecot filtermail filtermail-incoming nginx postfix unbound"
+
+# Optional services
+for svc in iroh-relay turnserver; do
+    systemctl is-enabled "$svc" 2>/dev/null && services="$services $svc"
+done
+
+exec systemctl is-active $services