Set up GitHub Actions for coding standards and tests

[yepzdk]

Add CI workflows for the project using the itk-dev GitHub Actions templates.

Scope

• Coding standards checks (PHP/Symfony, Twig, Markdown, JS/CSS as applicable).
• Run test suite on PRs.
• Align with itk-dev/devops_itkdev-docker and itk-dev GitHub Actions conventions.

Acceptance criteria

• CI runs coding-standards checks on PRs.
• CI runs the test suite on PRs.
• Reviewed and merged via PR.

Part of the Base setup milestone. Depends on the Docker + Symfony setup (#1).