feat: Add container registry support and Kustomize foundation

- Add registry secret template for private container registry authentication
- Fix frontend deployment to use imagePullSecrets for private registry
- Enhance deploy-k8s.sh with registry authentication handling
- Add PVC storage size validation to prevent storage reduction errors
- Add graceful StatefulSet update error handling
- Fix template variable substitution for DOCKER_IMAGE
- Remove conflicting static PVC file that had unprocessed template variables
- Add Kustomize structure as alternative to shell script templates:
  - Base configuration with common resources
  - Development overlay with dev-specific configurations
  - Support for environment-specific image tags and resource limits

Registry setup requires setting REGISTRY_USERNAME, REGISTRY_PASSWORD, and
optionally REGISTRY_HOST in .env file for private registry authentication.

k8s-kustomize/base/frontend-deployment.yaml

@@ -0,0 +1,45 @@
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: rxminder-frontend
+  labels:
+    component: frontend
+spec:
+  replicas: 1
+  selector:
+    matchLabels:
+      component: frontend
+  template:
+    metadata:
+      labels:
+        component: frontend
+    spec:
+      imagePullSecrets:
+        - name: rxminder-registry-secret
+      containers:
+        - name: frontend
+          image: frontend-image
+          ports:
+            - containerPort: 80
+          envFrom:
+            - configMapRef:
+                name: rxminder-config
+          resources:
+            requests:
+              memory: '32Mi'
+              cpu: '20m'
+            limits:
+              memory: '64Mi'
+              cpu: '40m'
+          livenessProbe:
+            httpGet:
+              path: /
+              port: 80
+            initialDelaySeconds: 30
+            periodSeconds: 30
+          readinessProbe:
+            httpGet:
+              path: /
+              port: 80
+            initialDelaySeconds: 5
+            periodSeconds: 5