feat: Add Helm chart for Kubernetes deployment (#1)

## Description

Add complete Helm chart for deploying the CV application to Kubernetes. The chart includes all necessary resources for a production-ready deployment with persistent storage and configurable authentication modes.

## Type of Change

- [x] `feat` - New feature (minor version bump)

## Breaking Changes

- [ ] This is a breaking change (major version bump)

**If breaking, describe the migration path:**

## Checklist

- [x] Commit messages follow [Conventional Commits](CONTRIBUTING.md#commit-guidelines)
- [x] Lint passes (`npm run lint`) - N/A for Helm charts
- [x] Build succeeds (`npm run build`) - N/A for Helm charts
- [x] Tests pass (`npm run test:run`) - N/A for Helm charts
- [ ] API documentation updated (if applicable)

## Testing

- `helm lint` passes on the chart
- `helm template test-release helm/cv-app/` renders 214 lines of valid Kubernetes manifests
- Verified all template helpers function correctly
- Tested conditional rendering (persistence enabled/disabled, simple/keycloak auth modes)

## Screenshots (if applicable)

N/A

## Related Issues

Implements the Helm chart design from `docs/plans/2026-02-23-helm-chart-design.md`

Co-authored-by: Tuan-Dat Tran <tuan-dat.tran@tudattr.dev>
Reviewed-on: #1

helm/cv-app/templates/backend-deployment.yaml

@@ -0,0 +1,80 @@
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: {{ include "cv-app.fullname" . }}-backend
+  labels:
+    {{- include "cv-app.labels" . | nindent 4 }}
+    app.kubernetes.io/component: backend
+spec:
+  replicas: {{ .Values.backend.replicaCount }}
+  selector:
+    matchLabels:
+      {{- include "cv-app.selectorLabels" . | nindent 6 }}
+      app.kubernetes.io/component: backend
+  template:
+    metadata:
+      annotations:
+        checksum/config: {{ include (print $.Template.BasePath "/configmap.yaml") . | sha256sum }}
+        checksum/secret: {{ include (print $.Template.BasePath "/secret.yaml") . | sha256sum }}
+        {{- with .Values.podAnnotations }}
+        {{- toYaml . | nindent 8 }}
+        {{- end }}
+      labels:
+        {{- include "cv-app.selectorLabels" . | nindent 8 }}
+        app.kubernetes.io/component: backend
+    spec:
+      {{- with .Values.imagePullSecrets }}
+      imagePullSecrets:
+        {{- toYaml . | nindent 8 }}
+      {{- end }}
+      serviceAccountName: {{ include "cv-app.serviceAccountName" . }}
+      securityContext:
+        {{- toYaml .Values.podSecurityContext | nindent 8 }}
+      containers:
+        - name: backend
+          securityContext:
+            {{- toYaml .Values.securityContext | nindent 12 }}
+          image: "{{ .Values.backend.image.repository }}:{{ .Values.backend.image.tag | default .Chart.AppVersion }}"
+          imagePullPolicy: {{ .Values.backend.image.pullPolicy }}
+          ports:
+            - name: http
+              containerPort: 3001
+              protocol: TCP
+          envFrom:
+            - configMapRef:
+                name: {{ include "cv-app.fullname" . }}-config
+            - secretRef:
+                name: {{ include "cv-app.fullname" . }}-secret
+          volumeMounts:
+            - name: data
+              mountPath: /app/data
+          livenessProbe:
+            httpGet:
+              path: /health
+              port: http
+          readinessProbe:
+            httpGet:
+              path: /health
+              port: http
+          resources:
+            {{- toYaml .Values.backend.resources | nindent 12 }}
+      volumes:
+        - name: data
+          {{- if .Values.persistence.enabled }}
+          persistentVolumeClaim:
+            claimName: {{ include "cv-app.fullname" . }}-data
+          {{- else }}
+          emptyDir: {}
+          {{- end }}
+      {{- with .Values.nodeSelector }}
+      nodeSelector:
+        {{- toYaml . | nindent 8 }}
+      {{- end }}
+      {{- with .Values.affinity }}
+      affinity:
+        {{- toYaml . | nindent 8 }}
+      {{- end }}
+      {{- with .Values.tolerations }}
+      tolerations:
+        {{- toYaml . | nindent 8 }}
+      {{- end }}