Refactor docker compose exec usage

Introduce centralized variables:
- docker_compose_command_base
- docker_compose_command_exec

Replaced hardcoded 'docker compose exec' with '{{ docker_compose_command_exec }}'
across multiple roles (BigBlueButton, EspoCRM, Friendica, Listmonk, Mailu, Matrix, OpenProject).
Ensures consistent environment file loading and reduces duplicated code.

Details: https://chatgpt.com/share/68d6a276-19d0-800f-839d-d191d97f7c41

roles/web-app-openproject/tasks/01_settings.yml

@@ -1,6 +1,6 @@
 - name: Set settings in OpenProject
   shell: >
-    docker compose exec {{ OPENPROJECT_WEB_SERVICE }} bash -c "cd /app &&
+    {{ docker_compose_command_exec }} {{ OPENPROJECT_WEB_SERVICE }} bash -c "cd /app &&
     RAILS_ENV={{ ENVIRONMENT | lower }} bundle exec rails runner \"Setting[:{{ item.key }}] = '{{ item.value }}'\""
   args:
     chdir: "{{ docker_compose.directories.instance }}"

roles/web-app-openproject/tasks/03_admin.yml

@@ -1,6 +1,6 @@
 - name: Ensure administrator user exists and is admin
   shell: >
-    docker compose exec web bash -c "
+    {{ docker_compose_command_exec }} web bash -c "
       cd /app &&
       RAILS_ENV={{ ENVIRONMENT | lower }} bundle exec rails runner \"
         u = User.find_by(login: '{{ OPENPROJECT_ADMINISTRATOR_USERNAME }}')