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/mysql/pvc.yaml

@@ -0,0 +1,13 @@
+apiVersion: v1
+kind: PersistentVolumeClaim
+metadata:
+  name: mysql-data-pvc
+  labels:
+    app.kubernetes.io/name: mysql
+    app.kubernetes.io/component: database
+spec:
+  accessModes:
+    - ReadWriteOnce
+  resources:
+    requests:
+      storage: 5Gi