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/build_matrix.py

@@ -0,0 +1,56 @@
+#!/usr/bin/env python3
+"""Parse meta/main.yml platforms and output a Docker test matrix as JSON."""
+
+import json
+import sys
+from pathlib import Path
+
+try:
+    import yaml
+except ImportError:
+    print("ERROR: PyYAML is required. Install with: pip install pyyaml", file=sys.stderr)
+    sys.exit(1)
+
+# Mapping Galaxy platform name -> Docker image prefix
+PLATFORM_IMAGE_MAP = {
+    "EL": "rockylinux",
+    "Debian": "debian",
+    "Ubuntu": "ubuntu",
+}
+
+def build_matrix(meta_path: str = "roles/remote_users_fact/meta/main.yml") -> list[dict]:
+    meta_file = Path(meta_path)
+    if not meta_file.exists():
+        print(f"ERROR: {meta_file} not found", file=sys.stderr)
+        sys.exit(1)
+
+    with open(meta_file) as f:
+        meta = yaml.safe_load(f)
+
+    platforms = meta.get("galaxy_info", {}).get("platforms", [])
+    if not platforms:
+        print("ERROR: No platforms found in meta/main.yml", file=sys.stderr)
+        sys.exit(1)
+
+    matrix = []
+    for platform in platforms:
+        name = platform["name"]
+        if name not in PLATFORM_IMAGE_MAP:
+            print(f"ERROR: Unknown platform '{name}'. Known: {list(PLATFORM_IMAGE_MAP.keys())}", file=sys.stderr)
+            sys.exit(1)
+
+        image_prefix = PLATFORM_IMAGE_MAP[name]
+        for version in platform.get("versions", []):
+            version_str = str(version)
+            slug = f"{name.lower()}{version_str}" if name == "EL" else f"{name.lower()}-{version_str}"
+            matrix.append({
+                "slug": slug,
+                "image": f"{image_prefix}:{version_str}",
+                "platform": name,
+                "version": version_str,
+            })
+
+    return matrix
+
+if __name__ == "__main__":
+    print(json.dumps(build_matrix(), indent=2))