[PavlosIsaris]

Summary

laravel-ci.yml had no database service, so a repository whose tests need MySQL or MariaDB could not use it. Mentorship-matching-backend is one example: a migration drops a primary key column, and its filter SQL uses MySQL date arithmetic. This PR adds an optional service.

• database-image (new input), for example mariadb:11.8 or mysql:8.4. The Backend tests and Browser tests jobs start it as a service on 127.0.0.1:3306 and wait for its health check. An empty value means no service, as before. SQLite needs none.
• database-name (new input, default testing): the database that the service creates.
• First step in both test jobs: it exports DB_HOST, DB_PORT, DB_DATABASE, DB_USERNAME and DB_PASSWORD. It stops with a clear message for an image that is not MySQL or MariaDB, and GitHub starts no container for such an image. pdo_mysql is added to the PHP extensions.
• DB_CONNECTION still comes from the caller's phpunit.xml or env file.
• New smoke jobs: laravel-mariadb and laravel-mysql run migrations against the service. They check the server, the version and the exported values with db:show --json.
• Docs: the guide, the template, AGENTS.md and the fixtures README describe the inputs. PostgreSQL is not supported.

GitHub documents the empty-image behaviour: "If jobs.<job_id>.services.<service_id>.image is assigned an empty string, the service will not start."

Related issues

None.

Checklist

• The change is limited to the topic in the title.
• Local checks pass: scripts/check-workflow-docs.py. actionlint and shellcheck run in the Self-check Lint job.
• Tests cover the new behaviour: the laravel-mariadb and laravel-mysql smoke jobs.
• Documentation is updated where the behaviour changed.
• No secrets or personal data are included.