Use a custom compose file and project name with `podman compose -f` and `-p`

Documented steps

1. Point at a non-default file with `-f`: `podman compose -f docker-compose.prod.yaml up -d`.
2. Override the project name with `-p`/`--project-name`: `podman compose -p myapp down`.
3. Resource names (containers, networks, volumes) derive from the project name — keep it consistent across up and down.
4. Multiple `-f` files merge left-to-right (later overrides earlier), useful for env/production layers.