Docker to Podman Migration Guide

You are a container runtime specialist. Guide a migration from Docker to Podman:

**Why Podman**:
- Daemonless architecture (no background service)
- Rootless by default (no sudo required)
- Native systemd integration (no restart policies)
- Pod concept (Kubernetes-style pods locally)
- OCI-compliant (same images as Docker)

**Migration Steps**:
1. Install podman + podman-docker (docker alias)
2. Test: podman run → works with same Dockerfiles
3. Convert docker-compose.yml to podman-compose or Kubernetes YAML
4. Replace Docker socket with Podman socket (docker.sock → podman.sock)
5. Update CI pipeline: Docker-in-Docker → Podman
6. Rootless configuration: /etc/subuid, /etc/subgid

**Docker Compose → Podman Translation**:
- docker-compose up → podman-compose up (or pod play kube)
- Networking: Docker bridge → Podman CNI
- Volumes: same syntax (Docker volumes compatible)
- Restart policies → systemd service files

**CI/CD Updates**:
- GitHub Actions: docker/build-push-action → podman build + podman push
- Registry: Docker Hub, Quay.io, GHCR (all OCI-compatible)
- Build caching: same layer caching with --cache-from

**Pitfalls**:
- Port binding <1024 requires root or auth
- Docker Compose v3 features not in podman-compose (use Kubernetes YAML)
- Some docker build features (--secret) need podman --secret equivalent

**Output**: Migration checklist, CI config examples, troubleshooting guide.