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/deployment.yaml

@@ -0,0 +1,74 @@
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: mysql
+  labels:
+    app.kubernetes.io/name: mysql
+    app.kubernetes.io/component: database
+spec:
+  replicas: 1
+  strategy:
+    type: Recreate # MySQL requires Recreate since PVC is ReadWriteOnce
+  selector:
+    matchLabels:
+      app.kubernetes.io/name: mysql
+      app.kubernetes.io/component: database
+  template:
+    metadata:
+      labels:
+        app.kubernetes.io/name: mysql
+        app.kubernetes.io/component: database
+    spec:
+      containers:
+        - name: mysql
+          image: mysql:8.0
+          ports:
+            - containerPort: 3306
+              name: mysql
+          env:
+            - name: MYSQL_ROOT_PASSWORD
+              valueFrom:
+                secretKeyRef:
+                  name: mysql-secret
+                  key: MYSQL_ROOT_PASSWORD
+            - name: MYSQL_DATABASE
+              valueFrom:
+                secretKeyRef:
+                  name: mysql-secret
+                  key: DB_NAME
+          volumeMounts:
+            - name: mysql-data
+              mountPath: /var/lib/mysql
+          resources:
+            requests:
+              cpu: 250m
+              memory: 512Mi
+            limits:
+              cpu: "1"
+              memory: 1Gi
+          livenessProbe:
+            exec:
+              command:
+                - mysqladmin
+                - ping
+                - -h
+                - localhost
+            initialDelaySeconds: 30
+            periodSeconds: 10
+            timeoutSeconds: 5
+            failureThreshold: 3
+          readinessProbe:
+            exec:
+              command:
+                - mysqladmin
+                - ping
+                - -h
+                - localhost
+            initialDelaySeconds: 10
+            periodSeconds: 5
+            timeoutSeconds: 3
+            failureThreshold: 5
+      volumes:
+        - name: mysql-data
+          persistentVolumeClaim:
+            claimName: mysql-data-pvc