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>

argocd-application.yaml

@@ -0,0 +1,35 @@
+# ArgoCD Application - GitOps deployment
+# kubectl apply -f argocd-application.yaml -n argocd
+apiVersion: argoproj.io/v1alpha1
+kind: Application
+metadata:
+  name: hell-world
+  namespace: argocd
+  finalizers:
+    - resources-finalizer.argocd.argoproj.io
+spec:
+  project: default
+
+  source:
+    # Gitea repository URL
+    repoURL: https://git.gecore.mn/admin/hell-world.git
+    targetRevision: HEAD
+    path: manifests
+
+  destination:
+    server: https://kubernetes.default.svc
+    namespace: hell-world
+
+  syncPolicy:
+    automated:
+      prune: true        # Устгагдсан resource-уудыг автоматаар устгана
+      selfHeal: true     # Гараар өөрчилсөн зүйлсийг автоматаар сэргээнэ
+    syncOptions:
+      - CreateNamespace=true
+      - PruneLast=true
+    retry:
+      limit: 5
+      backoff:
+        duration: 5s
+        factor: 2
+        maxDuration: 3m