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>

.woodpecker.yaml

@@ -0,0 +1,78 @@
+# Woodpecker CI Pipeline
+# Go Backend + Next.js Frontend + PostgreSQL
+
+when:
+  - event: [push, pull_request]
+    branch: main
+
+steps:
+  # 1. Backend Docker image build
+  build-backend:
+    image: docker:24-dind
+    privileged: true
+    commands:
+      - docker build -t hell-world-backend:${CI_COMMIT_SHA:0:8} ./backend
+      - docker tag hell-world-backend:${CI_COMMIT_SHA:0:8} registry.gecore.mn/library/hell-world-backend:${CI_COMMIT_SHA:0:8}
+      - docker tag hell-world-backend:${CI_COMMIT_SHA:0:8} registry.gecore.mn/library/hell-world-backend:latest
+
+  # 2. Frontend Docker image build
+  build-frontend:
+    image: docker:24-dind
+    privileged: true
+    commands:
+      - docker build -t hell-world-frontend:${CI_COMMIT_SHA:0:8} ./frontend
+      - docker tag hell-world-frontend:${CI_COMMIT_SHA:0:8} registry.gecore.mn/library/hell-world-frontend:${CI_COMMIT_SHA:0:8}
+      - docker tag hell-world-frontend:${CI_COMMIT_SHA:0:8} registry.gecore.mn/library/hell-world-frontend:latest
+
+  # 3. Push backend to Harbor registry
+  push-backend:
+    image: docker:24-dind
+    privileged: true
+    commands:
+      - echo "$HARBOR_PASSWORD" | docker login registry.gecore.mn -u "$HARBOR_USER" --password-stdin
+      - docker push registry.gecore.mn/library/hell-world-backend:${CI_COMMIT_SHA:0:8}
+      - docker push registry.gecore.mn/library/hell-world-backend:latest
+    secrets: [harbor_user, harbor_password]
+    when:
+      event: push
+      branch: main
+
+  # 4. Push frontend to Harbor registry
+  push-frontend:
+    image: docker:24-dind
+    privileged: true
+    commands:
+      - echo "$HARBOR_PASSWORD" | docker login registry.gecore.mn -u "$HARBOR_USER" --password-stdin
+      - docker push registry.gecore.mn/library/hell-world-frontend:${CI_COMMIT_SHA:0:8}
+      - docker push registry.gecore.mn/library/hell-world-frontend:latest
+    secrets: [harbor_user, harbor_password]
+    when:
+      event: push
+      branch: main
+
+  # 5. Update Kubernetes manifests with new image tags
+  update-manifests:
+    image: alpine:latest
+    commands:
+      - apk add --no-cache sed git
+      - sed -i "s|image:.*hell-world-backend.*|image: registry.gecore.mn/library/hell-world-backend:${CI_COMMIT_SHA:0:8}|g" manifests/backend-deployment.yaml
+      - sed -i "s|image:.*hell-world-frontend.*|image: registry.gecore.mn/library/hell-world-frontend:${CI_COMMIT_SHA:0:8}|g" manifests/frontend-deployment.yaml
+      - git config user.email "ci@gecore.mn"
+      - git config user.name "Woodpecker CI"
+      - git add manifests/
+      - git commit -m "ci: update images to ${CI_COMMIT_SHA:0:8}" || true
+      - git push origin main || true
+    when:
+      event: push
+      branch: main
+
+  # 6. Deploy notification
+  notify:
+    image: alpine:latest
+    commands:
+      - echo "✅ Build completed for commit ${CI_COMMIT_SHA:0:8}"
+      - echo "📦 Backend: registry.gecore.mn/library/hell-world-backend:${CI_COMMIT_SHA:0:8}"
+      - echo "📦 Frontend: registry.gecore.mn/library/hell-world-frontend:${CI_COMMIT_SHA:0:8}"
+      - echo "🔗 ArgoCD will sync automatically"
+    when:
+      status: [success, failure]