Add basic CI job

[bburda]

Feature request / General issue

Add basic CI

Proposal

Add a minimal GitHub Actions workflow that builds and tests ROS 2 packages on each push and pull request.
The workflow should:

• Set up ROS 2
• Install dependencies
• Run colcon build
• Run colcon test (and colcon test-result)

Motivation

• Ensures the package always builds and tests correctly
• Catches regressions early in pull requests
• Provides contributors with immediate feedback on their changes

Alternatives considered

• Running colcon build and tests only locally (easy to forget and inconsistent between developers)

Additional context

A single workflow file under .github/workflows/ci.yml is enough for a first version. More jobs (e.g. linting, multiple ROS 2 distros) can be added later.