chore(backup): change schedule from hourly to every 6 hours

Runs at 00:00, 06:00, 12:00, 18:00. Removes old hourly cron entry.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

roles/backup/tasks/main.yml

@@ -32,10 +32,17 @@
     group: root
     mode: "0750"
 
-- name: Schedule hourly backup
+- name: Remove old hourly backup cron (replaced by 6-hour schedule)
   ansible.builtin.cron:
     name: "Hourly services backup"
+    state: absent
+    user: root
+
+- name: Schedule backup every 6 hours
+  ansible.builtin.cron:
+    name: "Services backup every 6 hours"
     minute: "0"
+    hour: "0,6,12,18"
     job: "/usr/local/bin/backup-services >> /var/log/backup-services.log 2>&1"
     user: root
     state: present