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/namespace.yaml

@@ -0,0 +1,6 @@
+apiVersion: v1
+kind: Namespace
+metadata:
+  name: scrum-manager
+  labels:
+    app.kubernetes.io/part-of: scrum-manager