feat(scaling): enable horizontal scaling for API and worker pods

- Add unauthenticated /api/diagnostic/healthz/live and /healthz/ready
  probe endpoints for Kubernetes liveness/readiness checks
- Separate Celery Beat into dedicated beat service in docker-compose.yaml
- Remove container_name from api and worker services to allow scaling
- Create Helm beat-deployment.yaml for standalone Beat scheduler pod
- Remove -B flag from worker-deployment.yaml so workers can scale safely
- Add beat section and fix probe paths in Helm values.yaml
- Add tests for the new probe endpoints

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

helm/docuelevate/templates/beat-deployment.yaml

@@ -0,0 +1,83 @@
+{{- /*
+  Celery Beat scheduler — publishes periodic tasks to the broker.
+  Exactly ONE replica must run; never scale this deployment.
+*/ -}}
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: {{ include "docuelevate.fullname" . }}-beat
+  namespace: {{ .Release.Namespace }}
+  labels:
+    {{- include "docuelevate.labels" . | nindent 4 }}
+    app.kubernetes.io/component: beat
+spec:
+  replicas: 1
+  strategy:
+    type: Recreate          # Prevent two Beat instances from running simultaneously
+  selector:
+    matchLabels:
+      {{- include "docuelevate.selectorLabels" . | nindent 6 }}
+      app.kubernetes.io/component: beat
+  template:
+    metadata:
+      labels:
+        {{- include "docuelevate.selectorLabels" . | nindent 8 }}
+        app.kubernetes.io/component: beat
+      {{- with .Values.beat.podAnnotations }}
+      annotations:
+        {{- toYaml . | nindent 8 }}
+      {{- end }}
+    spec:
+      serviceAccountName: {{ include "docuelevate.serviceAccountName" . }}
+      {{- with .Values.imagePullSecrets }}
+      imagePullSecrets:
+        {{- toYaml . | nindent 8 }}
+      {{- end }}
+      {{- with .Values.beat.podSecurityContext }}
+      securityContext:
+        {{- toYaml . | nindent 8 }}
+      {{- end }}
+      containers:
+        - name: beat
+          image: {{ include "docuelevate.image" . }}
+          imagePullPolicy: {{ .Values.image.pullPolicy }}
+          command:
+            - celery
+            - -A
+            - app.celery_worker
+            - beat
+            - --loglevel=info
+          envFrom:
+            - configMapRef:
+                name: {{ include "docuelevate.fullname" . }}-config
+            - secretRef:
+                name: {{ include "docuelevate.fullname" . }}-secret
+          {{- with .Values.beat.securityContext }}
+          securityContext:
+            {{- toYaml . | nindent 12 }}
+          {{- end }}
+          resources:
+            {{- toYaml .Values.beat.resources | nindent 12 }}
+          volumeMounts:
+            - name: workdir
+              mountPath: /workdir
+      volumes:
+        - name: workdir
+          {{- if .Values.workdir.persistence.enabled }}
+          persistentVolumeClaim:
+            claimName: {{ .Values.workdir.persistence.existingClaim | default (printf "%s-workdir" (include "docuelevate.fullname" .)) }}
+          {{- else }}
+          emptyDir: {}
+          {{- end }}
+      {{- with .Values.beat.nodeSelector }}
+      nodeSelector:
+        {{- toYaml . | nindent 8 }}
+      {{- end }}
+      {{- with .Values.beat.affinity }}
+      affinity:
+        {{- toYaml . | nindent 8 }}
+      {{- end }}
+      {{- with .Values.beat.tolerations }}
+      tolerations:
+        {{- toYaml . | nindent 8 }}
+      {{- end }}

helm/docuelevate/templates/worker-deployment.yaml

@@ -42,7 +42,6 @@ spec:
             - -A
             - app.celery_worker
             - worker
-            - -B
             - --loglevel=info
             - -Q
             - document_processor,default,celery

helm/docuelevate/values.yaml

@@ -121,10 +121,10 @@ api:
     type: ClusterIP
     port: 8000
 
-  # Liveness / readiness probes
+  # Liveness / readiness probes (unauthenticated endpoints for kubelet)
   livenessProbe:
     httpGet:
-      path: /api/health
+      path: /api/diagnostic/healthz/live
       port: 8000
     initialDelaySeconds: 30
     periodSeconds: 20
@@ -132,7 +132,7 @@ api:
 
   readinessProbe:
     httpGet:
-      path: /api/health
+      path: /api/diagnostic/healthz/ready
       port: 8000
     initialDelaySeconds: 15
     periodSeconds: 10
@@ -191,7 +191,36 @@ worker:
       drop: ["ALL"]
 
 # ---------------------------------------------------------------------------
-# Shared workdir volume (api + worker mount the same PVC)
+# Celery Beat scheduler (singleton — always exactly 1 replica)
+# Beat publishes periodic tasks; workers consume them from the broker.
+# ---------------------------------------------------------------------------
+beat:
+  resources:
+    requests:
+      cpu: 100m
+      memory: 256Mi
+    limits:
+      cpu: 500m
+      memory: 512Mi
+
+  podAnnotations: {}
+  nodeSelector: {}
+  tolerations: []
+  affinity: {}
+
+  podSecurityContext:
+    runAsNonRoot: true
+    runAsUser: 1000
+    fsGroup: 1000
+
+  securityContext:
+    allowPrivilegeEscalation: false
+    readOnlyRootFilesystem: false
+    capabilities:
+      drop: ["ALL"]
+
+# ---------------------------------------------------------------------------
+# Shared workdir volume (api + worker + beat mount the same PVC)
 # ---------------------------------------------------------------------------
 workdir:
   persistence: