Podman doesn't support the `host-gateway` special value in extra_hosts,
which causes container startup failures on macOS with Podman Desktop.
Changes:
- Add docker-compose.docker.yml with extra_hosts override for Docker
- Update shannon script to detect Podman via `command -v podman`
- Skip extra_hosts override when Podman is detected
This ensures:
- Docker users (Linux): Get host.docker.internal working automatically
- Podman users (macOS): Base config works without modification
Co-authored-by: ajmallesh <ajmallesh@gmail.com>
