feat: add Kubernetes Kustomize deployment manifests

Add k8s/base/ directory with Kustomize manifests for deploying
the scrum-manager application to Kubernetes:

- Namespace (scrum-manager)
- MySQL: Deployment, Service, PVC, Secret
- Backend: Deployment (2 replicas) with init container, Service
- Frontend: Deployment (2 replicas), Service (NodePort), ConfigMap (nginx.conf)

All deployments include resource requests/limits, liveness/readiness
probes, and proper label selectors.

k8s/base/backend/service.yaml

@@ -0,0 +1,17 @@
+apiVersion: v1
+kind: Service
+metadata:
+  name: backend
+  labels:
+    app.kubernetes.io/name: backend
+    app.kubernetes.io/component: api
+spec:
+  type: ClusterIP
+  ports:
+    - port: 3001
+      targetPort: 3001
+      protocol: TCP
+      name: http
+  selector:
+    app.kubernetes.io/name: backend
+    app.kubernetes.io/component: api