Wire backup into setup_linux and add portainer1-jim backup host

Imports backup.yml from setup_linux.yml so the backup play is
reachable from the umbrella playbook via --tags backup. Also adds
a backup_hosts entry for portainer1-jim.im.lab (5GB, /data/compose).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

group_vars/all/backup.yml

@@ -16,3 +16,10 @@ backup_hosts:
     keep_daily: 7
     keep_weekly: 4
     keep_monthly: 6
+  portainer1-jim.im.lab:
+    storage_size_gb: 5
+    source_directories:
+      - /data/compose
+    keep_daily: 7
+    keep_weekly: 4
+    keep_monthly: 6