Create a ROS 2 (Lyrical Luth) ament_python package and build it with colcon

Documented steps

1. Source your ROS 2 installation: `source /opt/ros/lyrical/setup.bash` (Linux).
2. Go to your workspace's src directory, NOT the workspace root: `cd ~/ros2_ws/src`. Packages must live under src/.
3. Create the package: `ros2 pkg create --build-type ament_python --license Apache-2.0 --node-name my_node my_package`. This generates package.xml, resource/my_package, setup.cfg, setup.py, my_package/__init__.py, my_package/my_node.py and test/ files.
4. Verify the generated layout in ros2_ws/src/my_package: package.xml, resource, setup.cfg, setup.py, my_package/, test/.
5. Edit package.xml: fill in <description>, <maintainer email=...>, and <license> (e.g. <license>Apache-2.0</license>) - the generator leaves TODO placeholders.
6. Edit setup.py: set maintainer, maintainer_email, description and license to match package.xml exactly. name and version must also match between the two files.
7. Confirm setup.cfg contains [develop] script_dir=$base/lib/my_package and [install] install_scripts=$base/lib/my_package - this puts executables where `ros2 run` looks (lib/<pkg>).
8. Return to the workspace root: `cd ~/ros2_ws`.
9. Build everything with `colcon build`, or just this package with `colcon build --packages-select my_package`.
10. Open a NEW terminal, source the base install, then source the overlay from the workspace root: `source install/local_setup.bash`.
11. Run the generated executable: `ros2 run my_package my_node` - expect it to print `Hi from my_package.`
12. Official doc: https://docs.ros.org/en/lyrical/Tutorials/Beginner-Client-Libraries/Creating-Your-First-ROS2-Package.html