Fix unit test failures in Platform SDK integration

This commit fixes 4 failing unit tests after the Platform SDK integration:

1. Fixed 3 SecretAdapter tests (TestSecretAdapter_SDKMode,
   TestSecretAdapter_SDKMode_SecretNotReady,
   TestSecretAdapter_SDKMode_SecretVersioning) by adding PlatformConfig
   CRD scheme registration. The tests were failing with:
   "no kind is registered for the type v4.PlatformConfig in scheme"

2. Fixed TestApplyStandalone panic by adding nil check for sdkRuntime
   in getStandaloneStatefulSet. When sdkRuntime is nil (legacy tests),
   the function now falls back to getStandaloneStatefulSetLegacy which
   uses the pre-SDK implementation.

Changes:
- pkg/splunk/enterprise/secret_adapter_test.go: Import platformv4 and
  register PlatformConfig scheme in all SDK-mode tests
- pkg/splunk/enterprise/standalone.go: Add nil check and legacy
  fallback path in getStandaloneStatefulSet, add
  getStandaloneStatefulSetLegacy function for backward compatibility

All enterprise package tests now pass successfully.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: vivekr-splunk

pkg/splunk/enterprise/secret_adapter_test.go

@@ -15,6 +15,7 @@ import (
 	"sigs.k8s.io/controller-runtime/pkg/client/fake"
 
 	"github.com/go-logr/logr"
+	platformv4 "github.com/splunk/splunk-operator/api/platform/v4"
 	sdk "github.com/splunk/splunk-operator/pkg/platform-sdk"
 	"github.com/splunk/splunk-operator/pkg/platform-sdk/api/config"
 	splcommon "github.com/splunk/splunk-operator/pkg/splunk/common"
@@ -104,6 +105,7 @@ func TestSecretAdapter_SDKMode(t *testing.T) {
 	scheme := runtime.NewScheme()
 	_ = corev1.AddToScheme(scheme)
 	_ = config.AddToScheme(scheme)
+	_ = platformv4.AddToScheme(scheme)
 
 	// Create source secret (what admins create manually or via ESO)
 	sourceSecret := &corev1.Secret{
@@ -217,6 +219,7 @@ func TestSecretAdapter_SDKMode_SecretNotReady(t *testing.T) {
 	scheme := runtime.NewScheme()
 	_ = corev1.AddToScheme(scheme)
 	_ = config.AddToScheme(scheme)
+	_ = platformv4.AddToScheme(scheme)
 
 	// Create fake client WITHOUT source secret (simulating ExternalSecret not yet synced)
 	fakeClient := fake.NewClientBuilder().
@@ -292,6 +295,7 @@ func TestSecretAdapter_SDKMode_SecretVersioning(t *testing.T) {
 	scheme := runtime.NewScheme()
 	_ = corev1.AddToScheme(scheme)
 	_ = config.AddToScheme(scheme)
+	_ = platformv4.AddToScheme(scheme)
 
 	// Create source secret
 	sourceSecret := &corev1.Secret{

pkg/splunk/enterprise/standalone.go

@@ -294,6 +294,12 @@ func getStandaloneStatefulSet(ctx context.Context, client splcommon.ControllerCl
 	reqLogger := log.FromContext(ctx)
 	scopedLog := reqLogger.WithName("getStandaloneStatefulSet").WithValues("name", cr.GetName(), "namespace", cr.GetNamespace())
 
+	// Legacy mode: fall back to old implementation if SDK runtime is nil
+	if sdkRuntime == nil {
+		scopedLog.Info("Using legacy StatefulSet creation (SDK runtime not available)")
+		return getStandaloneStatefulSetLegacy(ctx, client, cr)
+	}
+
 	// Create SDK reconcile context
 	rctx := sdkRuntime.NewReconcileContext(ctx, cr.Namespace, cr.Name)
 
@@ -432,6 +438,27 @@ func getStandaloneStatefulSet(ctx context.Context, client splcommon.ControllerCl
 	return ss, nil
 }
 
+// getStandaloneStatefulSetLegacy returns a StatefulSet using the legacy (pre-SDK) implementation.
+// This is used for backward compatibility when SDK runtime is not available (e.g., in old tests).
+func getStandaloneStatefulSetLegacy(ctx context.Context, client splcommon.ControllerClient, cr *enterpriseApi.Standalone) (*appsv1.StatefulSet, error) {
+	// get generic statefulset for Splunk Enterprise objects
+	ss, err := getSplunkStatefulSet(ctx, client, cr, &cr.Spec.CommonSplunkSpec, SplunkStandalone, cr.Spec.Replicas, []corev1.EnvVar{})
+	if err != nil {
+		return nil, err
+	}
+
+	smartStoreConfigMap := getSmartstoreConfigMap(ctx, client, cr, SplunkStandalone)
+
+	if smartStoreConfigMap != nil {
+		setupInitContainer(&ss.Spec.Template, cr.Spec.Image, cr.Spec.ImagePullPolicy, commandForStandaloneSmartstore, cr.Spec.CommonSplunkSpec.EtcVolumeStorageConfig.EphemeralStorage)
+	}
+
+	// Setup App framework staging volume for apps
+	setupAppsStagingVolume(ctx, client, cr, &ss.Spec.Template, &cr.Spec.AppFrameworkConfig)
+
+	return ss, nil
+}
+
 // validateStandaloneSpec checks validity and makes default updates to a StandaloneSpec, and returns error if something is wrong.
 func validateStandaloneSpec(ctx context.Context, c splcommon.ControllerClient, cr *enterpriseApi.Standalone) error {
 	if cr.Spec.Replicas < 0 {