fix(ansible): replace deprecated entities and sync version requirements (#478)

* refactor(ansible): replace deprecated with_items and ansible facts

Replace deprecated `with_items` with `loop` keyword across all roles.
Migrate from legacy `ansible_*` top-level facts to `ansible_facts['*']`
syntax to prepare for ansible-core 2.24 where INJECT_FACTS_AS_VARS
will default to False.

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: Aleksei Sviridkin <f@lex.la>

* chore(ansible): sync minimum version requirements to 2.15

Align version checks in prereq and airgap roles with README requirement
of ansible-core 2.15+.

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: Aleksei Sviridkin <f@lex.la>

---------

Signed-off-by: Aleksei Sviridkin <f@lex.la>
Co-authored-by: Claude <noreply@anthropic.com>

roles/k3s_agent/tasks/main.yml

@@ -67,7 +67,7 @@
   ansible.builtin.lineinfile:
     path: "{{ systemd_dir }}/k3s-agent.service.env"
     line: "{{ item }}"
-  with_items: "{{ extra_service_envs }}"
+  loop: "{{ extra_service_envs }}"
 
 - name: Delete any existing token from the environment if different from the new one
   ansible.builtin.lineinfile:
@@ -80,7 +80,7 @@
   ansible.builtin.lineinfile:
     path: "{{ systemd_dir }}/k3s-agent.service.env"
     line: "{{ item }}"
-  with_items:
+  loop:
     - "K3S_TOKEN={{ token }}"
 
 - name: Modify ExecStart in k3s-agent.service to include API endpoint and extra args