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>

setup_linux.yml

@@ -101,4 +101,10 @@
 
     - name: Set system hostname to inventory_hostname
       ansible.builtin.hostname:
-        name: "{{ inventory_hostname }}"
+        name: "{{ inventory_hostname }}"
+
+# ==============================
+# FOURTH PLAY: BACKUP
+# ==============================
+
+- import_playbook: backup.yml