Add full-stack Hello World app with CI/CD

- Go backend with PostgreSQL connection
- Next.js frontend with TypeScript
- Docker Compose for local development
- Woodpecker CI pipeline for build and push
- Kubernetes manifests with Kustomize
- ArgoCD application for GitOps deployment

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

manifests/postgres-secret.yaml

@@ -0,0 +1,10 @@
+apiVersion: v1
+kind: Secret
+metadata:
+  name: postgres-secret
+  namespace: hell-world
+type: Opaque
+stringData:
+  POSTGRES_USER: postgres
+  POSTGRES_PASSWORD: postgres
+  POSTGRES_DB: hellodb