fix: use imageID in createAndStartContainer (closes #124)

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

internal/service/deploy/deploy.go

@@ -417,15 +417,13 @@ func (svc *Service) executeRollback(
 
 	svc.removeOldContainer(ctx, app, deployment)
 
-	rollbackOpts, err := svc.buildContainerOptions(ctx, app, deployment.ID)
+	rollbackOpts, err := svc.buildContainerOptions(ctx, app, previousImageID)
 	if err != nil {
 		svc.failDeployment(bgCtx, app, deployment, err)
 
 		return fmt.Errorf("failed to build container options: %w", err)
 	}
 
-	rollbackOpts.Image = previousImageID
-
 	containerID, err := svc.docker.CreateContainer(ctx, rollbackOpts)
 	if err != nil {
 		svc.failDeployment(bgCtx, app, deployment, fmt.Errorf("failed to create rollback container: %w", err))
@@ -1018,9 +1016,9 @@ func (svc *Service) createAndStartContainer(
 	ctx context.Context,
 	app *models.App,
 	deployment *models.Deployment,
-	_ string,
+	imageID string,
 ) (string, error) {
-	containerOpts, err := svc.buildContainerOptions(ctx, app, deployment.ID)
+	containerOpts, err := svc.buildContainerOptions(ctx, app, imageID)
 	if err != nil {
 		svc.failDeployment(ctx, app, deployment, err)
 
@@ -1064,7 +1062,7 @@ func (svc *Service) createAndStartContainer(
 func (svc *Service) buildContainerOptions(
 	ctx context.Context,
 	app *models.App,
-	deploymentID int64,
+	imageID string,
 ) (docker.CreateContainerOptions, error) {
 	envVars, err := app.GetEnvVars(ctx)
 	if err != nil {
@@ -1098,7 +1096,7 @@ func (svc *Service) buildContainerOptions(
 
 	return docker.CreateContainerOptions{
 		Name:    "upaas-" + app.Name,
-		Image:   fmt.Sprintf("upaas-%s:%d", app.Name, deploymentID),
+		Image:   imageID,
 		Env:     envMap,
 		Labels:  buildLabelMap(app, labels),
 		Volumes: buildVolumeMounts(volumes),