fix: resolve Jinja2 .keys ambiguity, fastfetch availability, and python interpreter

- Use bracket notation item['keys'] instead of item.keys to avoid
  conflict with Python dict .keys() method
- Remove fastfetch from Debian 12 package list (only available in 13+)
- Set explicit python interpreter path for post-reboot tasks

main.yml

@@ -152,6 +152,7 @@
         ansible_password: "{{ system_cfg.users[0].password }}"
         ansible_become_password: "{{ system_cfg.users[0].password }}"
         ansible_ssh_extra_args: "-o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no"
+        ansible_python_interpreter: /usr/bin/python3
 
     - name: Install post-reboot packages
       when: