fix: add publicUrl to volume server for host network access

- Add -publicUrl=localhost:8080 to volume server command
- Ensures filer returns localhost URL instead of Docker service name
- Fixes UnknownHostException when tests run on host network
- Volume server is accessible via localhost from CI runner

test/java/spark/docker-compose.yml

@@ -27,7 +27,7 @@ services:
     ports:
       - "8080:8080"
       - "18080:18080"
-    command: "volume -mserver=seaweedfs-master:9333 -ip=seaweedfs-volume -ip.bind=0.0.0.0 -port=8080 -port.grpc=18080 -preStopSeconds=1"
+    command: "volume -mserver=seaweedfs-master:9333 -ip=seaweedfs-volume -ip.bind=0.0.0.0 -port=8080 -port.grpc=18080 -publicUrl=localhost:8080 -preStopSeconds=1"
     depends_on:
       seaweedfs-master:
         condition: service_healthy