fix: use explicit $HOME path for Maven mount and add verification

Issue: docker-compose was using ~ which may not expand correctly in CI

Changes:
1. docker-compose.yml: Changed ~/.m2 to ${HOME}/.m2
   - Ensures proper path expansion in GitHub Actions
   - $HOME is /home/runner in GitHub Actions runners

2. Added verification step in workflow:
   - Lists all SNAPSHOT artifacts before tests
   - Shows what's available in Maven local repo
   - Will help diagnose if artifacts aren't being restored correctly

This should ensure the Maven container can access the locally built
3.80.1-SNAPSHOT JARs with our debug logging code.

test/java/spark/docker-compose.yml

@@ -71,7 +71,7 @@ services:
     container_name: seaweedfs-spark-tests
     volumes:
       - .:/workspace
-      - ~/.m2:/root/.m2
+      - ${HOME}/.m2:/root/.m2
     working_dir: /workspace
     environment:
       - SEAWEEDFS_TEST_ENABLED=true