feat(security): add auditd/journald/logrotate role

Port Modules/Security/secharden-audit-agents.sh.

Deploys hardened configurations for:
- auditd (log rotation, disk space actions, email alerts)
- systemd-journald (persistent storage)
- logrotate (weekly rotation, 4 weeks retention)

This role is disabled by default (run_security_audit: false) matching
the legacy script which was commented out of the run order.

🤖 Generated with [Crush](https://github.com/charmassociates/crush)

Assisted-by: GLM-5 via Crush <crush@charm.land>

roles/security_audit/handlers/main.yml

@@ -0,0 +1,10 @@
+---
+- name: Restart auditd
+  ansible.builtin.systemd:
+    name: auditd
+    state: restarted
+
+- name: Restart journald
+  ansible.builtin.systemd:
+    name: systemd-journald
+    state: restarted