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/overlays/dev/kustomization.yaml

@@ -0,0 +1,83 @@
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+
+metadata:
+  name: rxminder-dev
+
+namespace: rxminder-dev
+
+resources:
+  - ../../base
+
+# Development-specific labels
+commonLabels:
+  environment: dev
+
+# Override images for development
+images:
+  - name: frontend-image
+    newName: gitea-http.taildb3494.ts.net/will/rxminder
+    newTag: dev
+  - name: couchdb-image
+    newName: couchdb
+    newTag: 3.3.2
+
+# Development replicas (lower for resource conservation)
+replicas:
+  - name: rxminder-frontend
+    count: 1
+
+# Development-specific patches
+patches:
+  - target:
+      kind: Deployment
+      name: rxminder-frontend
+    patch: |-
+      - op: replace
+        path: /spec/template/spec/containers/0/resources/requests/memory
+        value: "16Mi"
+      - op: replace
+        path: /spec/template/spec/containers/0/resources/limits/memory
+        value: "32Mi"
+      - op: add
+        path: /spec/template/spec/containers/0/env
+        value:
+          - name: NODE_ENV
+            value: "development"
+          - name: LOG_LEVEL
+            value: "debug"
+
+  - target:
+      kind: Ingress
+      name: rxminder-ingress
+    patch: |-
+      - op: replace
+        path: /spec/rules/0/host
+        value: "rxminder-dev.local"
+
+  - target:
+      kind: PersistentVolumeClaim
+      name: rxminder-couchdb-pvc
+    patch: |-
+      - op: replace
+        path: /spec/resources/requests/storage
+        value: "1Gi"
+
+# Development-specific ConfigMap
+configMapGenerator:
+  - name: rxminder-config
+    literals:
+      - NODE_ENV=development
+      - API_URL=http://rxminder-couchdb-service:5984
+      - LOG_LEVEL=debug
+      - DEBUG=true
+    behavior: replace
+
+# Development secrets (use weak passwords for dev)
+secretGenerator:
+  - name: couchdb-secret
+    literals:
+      - username=admin
+      - password=devpass123
+    type: Opaque
+    behavior: replace