feat(ci): add multi-platform CI testing via Docker

Add CI infrastructure that tests the Ansible role on every distro
declared in meta/main.yml (EL 8/9, Debian bullseye/bookworm,
Ubuntu focal/jammy/noble) using Docker containers.

- ci/build_matrix.py: parse meta/main.yml platforms into JSON matrix
- ci/test_playbook.yml: test playbook (state=present + validate)
- ci/Dockerfile.el, ci/Dockerfile.debian: per-family Docker images
- Makefile: orchestrator (make test, make test-<slug>, make lint)
- .gitea/workflows/ci.yml: Gitea Actions with dynamic matrix
- .gitlab-ci.yml: GitLab CI pipeline
- Jenkinsfile: Jenkins pipeline with parallel stages
- .yamllint.yml: linter configuration
- .dockerignore: exclude .git and CI configs from Docker context

ci/test_playbook.yml

@@ -0,0 +1,17 @@
+---
+# ci/test_playbook.yml — Playbook de test CI
+# Execute le role avec state=present et validation complete
+
+- name: Test remote_users_fact
+  hosts: localhost
+  connection: local
+  become: true
+  gather_facts: true
+
+  vars:
+    remote_users_fact_state: present
+    remote_users_fact_validate: true
+    remote_users_fact_display_summary: true
+
+  roles:
+    - role: remote_users_fact