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/kustomization.yaml

@@ -0,0 +1,25 @@
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+
+namespace: scrum-manager
+
+labels:
+  - pairs:
+      app.kubernetes.io/part-of: scrum-manager
+      app.kubernetes.io/managed-by: kustomize
+    includeSelectors: true
+
+resources:
+  - namespace.yaml
+  # MySQL
+  - mysql/secret.yaml
+  - mysql/pvc.yaml
+  - mysql/deployment.yaml
+  - mysql/service.yaml
+  # Backend
+  - backend/deployment.yaml
+  - backend/service.yaml
+  # Frontend
+  - frontend/configmap.yaml
+  - frontend/deployment.yaml
+  - frontend/service.yaml