fix(system_docker): fix daemon.json corruption on re-run

Two bugs caused daemon.json to be overwritten with invalid content:
- Invalid `when` condition using unsupported Ansible inline stat syntax,
  causing the existing file read to be silently skipped and docker_config
  to always reset to {}
- Folded scalar `>` in set_fact converted the dict to a Python string
  representation, which to_nice_json serialized as a JSON string instead
  of an object

Fixes identified during 2026-04-13 power cut incident post-mortem.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ansible/arcodange/factory/playbooks/system/system_docker.yml

@@ -35,12 +35,16 @@
         state: directory
         mode: '0755'
 
+    - name: Check if daemon.json exists
+      ansible.builtin.stat:
+        path: /etc/docker/daemon.json
+      register: docker_config_stat
+
     - name: Lire la configuration Docker existante
       ansible.builtin.command: "cat /etc/docker/daemon.json"
       register: docker_config_raw
-      ignore_errors: yes
       changed_when: false
-      when: (ansible.builtin.stat.path='/etc/docker/daemon.json').stat.exists
+      when: docker_config_stat.stat.exists
 
     - name: Initialiser la variable de config Docker
       ansible.builtin.set_fact:
@@ -82,12 +86,7 @@
 
     - name: Ensure docker_config is a dictionary
       ansible.builtin.set_fact:
-        docker_config: >
+        docker_config: "{{ docker_config if docker_config is mapping else {} }}"
-          {% if docker_config is mapping %}
-            {{ docker_config }}
-          {% else %}
-            {}
-          {% endif %}
 
     - name: Écrire la configuration mise à jour
       ansible.builtin.copy: