Add Kubernetes deployment manifests (Deployment, Service, ConfigMap, Secret)

[treblereel]

Context

Part of epic #1 — Build production-ready REST microservice with k8s deployment on top of casehub-engine. After Docker image is built (issue #13), need Kubernetes manifests for deploying the service with proper configuration, health checks, and resource management.

What

Create Kubernetes deployment manifests:

• Deployment manifest with liveness/readiness probes, resource limits, multiple replicas
• Service manifest (ClusterIP or LoadBalancer)
• ConfigMap for non-sensitive configuration
• Secret example for database credentials
• PostgreSQL deployment example (StatefulSet or external DB reference)

Acceptance Criteria

• Deployment manifest includes liveness probe pointing to /q/health/live
• Deployment manifest includes readiness probe pointing to /q/health/ready
• Resource requests and limits defined (e.g., CPU: 500m/1000m, memory: 512Mi/1Gi)
• Deployment supports multiple replicas (default: 2) for stateless operation
• ConfigMap contains non-sensitive env vars (DB_HOST, DB_PORT, DLQ_ENABLED, etc.)
• Secret example shows secure credential injection (DB_USERNAME, DB_PASSWORD)
• Service manifest exposes port 8080 for HTTP traffic
• PostgreSQL StatefulSet or external database connection example provided
• All manifests valid and deployable with kubectl apply -f k8s/

Notes

• Manifests should go in k8s/ or deploy/k8s/ directory
• Use environment variables from ConfigMap/Secret (issue Add production configuration profile with environment variables #9)
• Graceful shutdown: set terminationGracePeriodSeconds appropriately
• Consider adding HorizontalPodAutoscaler example (can be follow-up)
• PostgreSQL can be external managed service or in-cluster StatefulSet for dev
• File paths: k8s/deployment.yaml, k8s/service.yaml, k8s/configmap.yaml, k8s/secret-example.yaml, k8s/postgres.yaml