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/secret.yaml

@@ -0,0 +1,17 @@
+apiVersion: v1
+kind: Secret
+metadata:
+  name: mysql-secret
+  labels:
+    app.kubernetes.io/name: mysql
+    app.kubernetes.io/component: database
+type: Opaque
+data:
+  # Base64 encoded values — change these for production!
+  # echo -n 'scrumpass' | base64 => c2NydW1wYXNz
+  # echo -n 'root' | base64 => cm9vdA==
+  # echo -n 'scrum_manager' | base64 => c2NydW1fbWFuYWdlcg==
+  MYSQL_ROOT_PASSWORD: c2NydW1wYXNz
+  DB_USER: cm9vdA==
+  DB_PASSWORD: c2NydW1wYXNz
+  DB_NAME: c2NydW1fbWFuYWdlcg==