feat(global_defaults): add root.shell to system schema and normalization

roles/global_defaults/tasks/_normalize_system.yml

@@ -84,6 +84,7 @@
       users: "{{ system_raw.users | default([]) }}"
       root:
         password: "{{ system_raw.root.password | string }}"
+        shell: "{{ system_raw.root.shell | default('/bin/bash') | string }}"
       # --- LUKS disk encryption ---
       luks:
         enabled: "{{ system_raw.luks.enabled | bool }}"