test(infra): add VirtualBox inventory and fix ansible.cfg

- Add VirtualBox test cluster inventory (3 VMs: 1 manager + 2 workers)
- Fix ansible.cfg callback plugin (use ansible.builtin.default)
- Verified connectivity to all VMs via SSH
- All VMs running Ubuntu 22.04.5 LTS on x86_64
- KVM available on all nodes

VirtualBox VMs:
- swarm-manager: 192.168.56.10 (2 vCPU, 2GB RAM)
- swarm-worker-1: 192.168.56.11 (2 vCPU, 4GB RAM)
- swarm-worker-2: 192.168.56.12 (2 vCPU, 4GB RAM)

Tested:
✅ ansible all -m ping — All 3 nodes reachable
✅ KVM device present on all nodes
✅ Architecture verified (x86_64)
✅ OS verified (Ubuntu 22.04.5 LTS)

Author: restuhaqza

infrastructure/ansible/ansible.cfg

@@ -9,7 +9,7 @@ fact_caching_connection = /tmp/ansible_facts
 fact_caching_timeout = 86400
 
 # Output formatting
-stdout_callback = yaml
+stdout_callback = ansible.builtin.default
 callback_whitelist = profile_tasks, timer
 
 # SSH settings

infrastructure/ansible/inventory/virtualbox/hosts

@@ -0,0 +1,18 @@
+# SwarmCracker Test Cluster - VirtualBox
+
+[managers]
+swarm-manager ansible_host=192.168.56.10 ansible_ssh_private_key_file=/home/kali/.openclaw/workspace/projects/swarmcracker/test-automation/.vagrant/machines/manager/virtualbox/private_key
+
+[workers]
+swarm-worker-1 ansible_host=192.168.56.11 ansible_ssh_private_key_file=/home/kali/.openclaw/workspace/projects/swarmcracker/test-automation/.vagrant/machines/worker1/virtualbox/private_key
+swarm-worker-2 ansible_host=192.168.56.12 ansible_ssh_private_key_file=/home/kali/.openclaw/workspace/projects/swarmcracker/test-automation/.vagrant/machines/worker2/virtualbox/private_key
+
+[swarmcracker:children]
+managers
+workers
+
+[swarmcracker:vars]
+ansible_user=vagrant
+ansible_become=yes
+ansible_become_method=sudo
+ansible_ssh_common_args='-o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null'