Wire the imageID parameter (returned from docker build) through
createAndStartContainer and buildContainerOptions instead of
reconstructing a mutable tag via fmt.Sprintf.
This ensures containers reference the immutable image digest,
avoiding tag-reuse races when deploys overlap.
Changes:
- Rename _ string to imageID string in createAndStartContainer
- Change buildContainerOptions to accept imageID string instead of deploymentID int64
- Use imageID directly as the Image field in container options
- Update rollback path to pass previousImageID directly
- Add test verifying imageID flows through to container options
- Add database.NewTestDatabase and logger.NewForTest test helpers
