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>

docker-compose.yml

@@ -0,0 +1,46 @@
+services:
+  postgres:
+    image: postgres:16-alpine
+    container_name: hello-postgres
+    environment:
+      POSTGRES_USER: postgres
+      POSTGRES_PASSWORD: postgres
+      POSTGRES_DB: hellodb
+    ports:
+      - "5432:5432"
+    volumes:
+      - postgres_data:/var/lib/postgresql/data
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U postgres"]
+      interval: 5s
+      timeout: 5s
+      retries: 5
+
+  backend:
+    build: ./backend
+    container_name: hello-backend
+    ports:
+      - "8080:8080"
+    environment:
+      DB_HOST: postgres
+      DB_PORT: 5432
+      DB_USER: postgres
+      DB_PASSWORD: postgres
+      DB_NAME: hellodb
+      PORT: 8080
+    depends_on:
+      postgres:
+        condition: service_healthy
+
+  frontend:
+    build: ./frontend
+    container_name: hello-frontend
+    ports:
+      - "3000:3000"
+    environment:
+      NEXT_PUBLIC_API_URL: http://localhost:8080
+    depends_on:
+      - backend
+
+volumes:
+  postgres_data: