feat(k8s): add HelmService and rewrite deleteApplication

- New HelmService wrapping Helm CLI (install/upgrade, rollback, uninstall, history, status)
- deleteApplication: helm uninstall + explicit cleanup of kept PVCs, secrets, TLS certs
- buildHelmValues: include registry.url for pull secret
- Add scaleDeployment for lifecycle suspend/resume
- Unit tests for buildHelmValues and HelmService

backend/src/kubernetes/kubernetes.module.ts

@@ -1,10 +1,11 @@
 import { Module, forwardRef } from '@nestjs/common';
 import { KubernetesService } from './kubernetes.service';
+import { HelmService } from './helm.service';
 import { ClustersModule } from '../clusters/clusters.module';
 
 @Module({
   imports: [forwardRef(() => ClustersModule)],
-  providers: [KubernetesService],
-  exports: [KubernetesService],
+  providers: [KubernetesService, HelmService],
+  exports: [KubernetesService, HelmService],
 })
 export class KubernetesModule {}