fix: apply review feedback on Docker storage and security documentation

- Fix storage_ip derivation to use default route first, not Swarm RemoteManagers
- Make iSCSI container entrypoint idempotent (check before create for target/LUN/bind)
- Pin erichough/nfs-server from 'latest' to '2.2.1' for reproducibility
- Replace curl|sh Docker install with apt repo in Dockerfile.test
- Add docker.sock security warnings in docker-compose.test.yml and CI workflow
- Update stale 'storage VM' references in comments and .env.test.example"

Co-authored-by: GoodOlClint <151449+GoodOlClint@users.noreply.github.com>
Agent-Logs-Url: https://github.com/GoodOlClint/PSProxmoxVE/sessions/534c0a63-2988-496c-b0ae-e291fcfa050b

tests/docker-compose.test.yml

@@ -38,6 +38,8 @@ services:
     volumes:
       - ..:/repo
       - /opt/pve-isos:/opt/pve-isos
+      # WARNING: Mounting the Docker socket grants this container root-equivalent
+      # access to the host's Docker daemon. Only use on trusted, isolated machines.
       - /var/run/docker.sock:/var/run/docker.sock
     working_dir: /repo
     stdin_open: true