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/files/journald.conf

@@ -0,0 +1,31 @@
+[Journal]
+#Compress=yes
+#Seal=yes
+#SplitMode=uid
+#SyncIntervalSec=5m
+#RateLimitIntervalSec=30s
+#RateLimitBurst=10000
+#SystemMaxUse=
+#SystemKeepFree=
+#SystemMaxFileSize=
+#SystemMaxFiles=100
+#RuntimeMaxUse=
+#RuntimeKeepFree=
+#RuntimeMaxFileSize=
+#RuntimeMaxFiles=100
+#MaxRetentionSec=
+#MaxFileSec=1month
+#ForwardToSyslog=yes
+#ForwardToKMsg=no
+#ForwardToConsole=no
+#ForwardToWall=yes
+#TTYPath=/dev/console
+#MaxLevelStore=debug
+#MaxLevelSyslog=debug
+#MaxLevelKMsg=notice
+#MaxLevelConsole=info
+#MaxLevelWall=emerg
+#LineMax=48K
+#ReadKMsg=yes
+#Audit=no
+Storage=persistent