refactor: consolidate all roles into ansible/roles/ and update ansible.cfg

- Move all roles from playbooks/roles/ to roles/
- Update roles_path in ansible.cfg
- Add cast user to common role
- Create standalone podman role
- Add semaphore role with Podman + Quadlet support

ansible/roles/observer/files/prometheus_alerts_rules.yml

@@ -0,0 +1,11 @@
+groups:
+- name: AllInstances
+  rules:
+  - alert: InstanceDown
+    expr: up == 0
+    for: 1m
+    annotations:
+      title: 'Instance {{ $labels.instance }} down'
+      description: '{{ $labels.instance }} of job {{ $labels.job }} has been down for more than 1 minute.'
+    labels:
+      severity: 'critical'