Fix ACME DNS resolution failures in the caddy container

The host's systemd-resolved stub (127.0.0.53) is unreachable from inside
the container network namespace, so Caddy could not resolve Let's Encrypt
endpoints. Point it at public resolvers instead.

docker-compose.yml

@@ -64,6 +64,11 @@ services:
     ports:
       - "80:80"
       - "443:443"
+    # Host uses systemd-resolved (127.0.0.53), unreachable from inside the
+    # container network namespace; ACME lookups need a real resolver.
+    dns:
+      - 1.1.1.1
+      - 8.8.8.8
     environment:
       PUBLIC_DOMAIN: ${PUBLIC_DOMAIN}
       CMS_DOMAIN: ${CMS_DOMAIN}