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/backend-deployment.yaml

@@ -0,0 +1,64 @@
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: backend
+  namespace: hell-world
+  labels:
+    app: backend
+spec:
+  replicas: 2
+  selector:
+    matchLabels:
+      app: backend
+  template:
+    metadata:
+      labels:
+        app: backend
+    spec:
+      containers:
+        - name: backend
+          image: registry.gecore.mn/library/hell-world-backend:latest
+          ports:
+            - containerPort: 8080
+              name: http
+          env:
+            - name: DB_HOST
+              value: postgres
+            - name: DB_PORT
+              value: "5432"
+            - name: DB_USER
+              valueFrom:
+                secretKeyRef:
+                  name: postgres-secret
+                  key: POSTGRES_USER
+            - name: DB_PASSWORD
+              valueFrom:
+                secretKeyRef:
+                  name: postgres-secret
+                  key: POSTGRES_PASSWORD
+            - name: DB_NAME
+              valueFrom:
+                secretKeyRef:
+                  name: postgres-secret
+                  key: POSTGRES_DB
+            - name: PORT
+              value: "8080"
+          resources:
+            requests:
+              memory: "64Mi"
+              cpu: "50m"
+            limits:
+              memory: "128Mi"
+              cpu: "100m"
+          livenessProbe:
+            httpGet:
+              path: /api/health
+              port: 8080
+            initialDelaySeconds: 10
+            periodSeconds: 10
+          readinessProbe:
+            httpGet:
+              path: /api/health
+              port: 8080
+            initialDelaySeconds: 5
+            periodSeconds: 5