Tag built images with the commit's short hash (closes #239)

Builds are tagged upaas-<app>:<short hash>, git's own short form of
the commit checked out, instead of the deployment number.

A redeploy of a commit gives the tag to the new image. The cleanup
after a deploy now also finds the app's untagged images among those
its deployments recorded, and removes them by ID once the app neither
runs them nor would roll back to them. It keeps every image any app
uses, since apps that build the same commit can share one.

The clone reads the commits from git's output after removing Docker's
log headers, which had hidden the COMMIT: line; commit_sha is now
saved on update so manual deploys keep the commit they recorded.

Model: opus-5-5

internal/models/deployment.go

@@ -203,11 +203,12 @@ func (d *Deployment) insert(ctx context.Context) error {
 func (d *Deployment) update(ctx context.Context) error {
 	query := `
 		UPDATE deployments SET
-			image_id = ?, container_id = ?, status = ?, logs = ?, finished_at = ?
+			commit_sha = ?, image_id = ?, container_id = ?, status = ?, logs = ?,
+			finished_at = ?
 		WHERE id = ?`
 
 	_, err := d.db.Exec(ctx, query,
-		d.ImageID, d.ContainerID, d.Status, d.Logs, d.FinishedAt, d.ID,
+		d.CommitSHA, d.ImageID, d.ContainerID, d.Status, d.Logs, d.FinishedAt, d.ID,
 	)
 
 	return err
@@ -295,6 +296,45 @@ func FindDeploymentsByAppID(
 	return deployments, nil
 }
 
+// FindDeploymentImageIDs returns the IDs of the images an app's
+// deployments built or rolled back to.
+func FindDeploymentImageIDs(
+	ctx context.Context,
+	deployDB *database.Database,
+	appID string,
+) ([]string, error) {
+	rows, err := deployDB.Query(ctx, `
+		SELECT DISTINCT image_id FROM deployments
+		WHERE app_id = ? AND image_id IS NOT NULL`,
+		appID,
+	)
+	if err != nil {
+		return nil, fmt.Errorf("querying deployment image IDs: %w", err)
+	}
+
+	defer func() { _ = rows.Close() }()
+
+	var imageIDs []string
+
+	for rows.Next() {
+		var imageID string
+
+		scanErr := rows.Scan(&imageID)
+		if scanErr != nil {
+			return nil, fmt.Errorf("scanning deployment image ID: %w", scanErr)
+		}
+
+		imageIDs = append(imageIDs, imageID)
+	}
+
+	rowsErr := rows.Err()
+	if rowsErr != nil {
+		return nil, fmt.Errorf("iterating deployment image IDs: %w", rowsErr)
+	}
+
+	return imageIDs, nil
+}
+
 // LatestDeploymentForApp finds the most recent deployment for an app.
 //
 //nolint:nilnil // returning nil,nil is idiomatic for "not found" in Active Record