Skip the layout guard under --check

Under --check the git task reports "changed" without writing anything, so on a
host that has not been deployed yet there is no checkout to stat and the guard
fired on a perfectly fine configuration - making `just check mediapis.yml
musicdolphin` fail before the first real run.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

roles/pi_musicmouse/tasks/main.yml

@@ -46,6 +46,9 @@
   ansible.builtin.stat:
     path: /opt/musicmouse/python-backend/pyproject.toml
   register: pi_musicmouse_pyproject
+  # Meaningless under --check on a host that has never been deployed: the git task
+  # above reports "changed" without writing anything, so there is nothing to stat.
+  when: not ansible_check_mode
 
 - name: Fail on a pre-rearchitecture checkout
   ansible.builtin.fail:
@@ -57,7 +60,7 @@
       mediapi_install_kidsmusic to false for this host and leave whatever is installed
       alone. Stopping here rather than failing three tasks deeper with the real reason
       buried.
-  when: not pi_musicmouse_pyproject.stat.exists
+  when: not ansible_check_mode and not pi_musicmouse_pyproject.stat.exists
 
 - name: Create virtualenv with Python {{ pi_musicmouse_python_version }}
   ansible.builtin.command: