Support running `vp run` with Podman when Docker is unavailable

[nezhar]

Summary

vp run pi fails when Docker is not installed, even if Podman is available.

Environment

• Podman version: 5.7.0
• Context: running in a Python virtual environment on Linux

Reproduction

(venv) root@v220:~/DEV/VibePod# vp
 run pi
Docker is not available: Error while fetching
server API version: ('Connection aborted.',
FileNotFoundError(2, 'No such file or
directory'))

Expected behavior

vp run pi should run without requiring Docker when Podman is installed and available.

Actual behavior

The CLI attempts to use Docker and exits with an error when Docker is not available.

Proposed direction

• Detect Podman availability and support it as a first-class runtime backend.
• Allow vp run to execute with Podman when Docker is missing.
• Improve error messaging to suggest Podman fallback or configuration options.

[nezhar]

Fixed by enabling the podman.socket

systemctl --user enable --now podman.socket                                  
export DOCKER_HOST=unix:///run/user/$(id -u)/podman/podman.sock

Docs extended in #98