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

roles/bootstrap/vars/main.yml

@@ -104,7 +104,7 @@ bootstrap_debian_extra_common:
 bootstrap_debian_extra_versioned:
   - linux-image-amd64
   - "{{ 'duf' if (os_version | string) not in ['10', '11'] else '' }}"
-  - "{{ 'fastfetch' if (os_version | string) in ['12', '13', 'unstable'] else '' }}"
+  - "{{ 'fastfetch' if (os_version | string) in ['13', 'unstable'] else '' }}"
   - "{{ 'neofetch' if (os_version | string) == '12' else '' }}"
   - "{{ 'software-properties-common' if (os_version | string) not in ['13', 'unstable'] else '' }}"
   - "{{ 'systemd-zram-generator' if (os_version | string) not in ['10', '11'] else '' }}"