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/service/deploy/deploy_cleanup_test.go

@@ -20,7 +20,7 @@ func TestCleanupCancelledDeploy_RemovesBuildDir(t *testing.T) {
 	tmpDir := t.TempDir()
 	cfg := &config.Config{DataDir: tmpDir}
 
-	svc := deploy.NewTestServiceWithConfig(slog.Default(), cfg, nil)
+	svc := deploy.NewTestServiceWithConfig(slog.Default(), cfg, nil, nil)
 
 	// Create a fake build directory matching the deployment pattern
 	appName := "test-app"
@@ -59,7 +59,7 @@ func TestCleanupCancelledDeploy_NoBuildDir(t *testing.T) {
 	tmpDir := t.TempDir()
 	cfg := &config.Config{DataDir: tmpDir}
 
-	svc := deploy.NewTestServiceWithConfig(slog.Default(), cfg, nil)
+	svc := deploy.NewTestServiceWithConfig(slog.Default(), cfg, nil, nil)
 
 	// Should not panic when build dir doesn't exist
 	svc.CleanupCancelledDeploy(context.Background(), "nonexistent-app", 1, "")