feat: remove Helm-managed Secret template

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

helm/shorefront/templates/secret.yaml

@@ -1,11 +0,0 @@
-apiVersion: v1
-kind: Secret
-metadata:
-  name: shorefront-secret
-  namespace: {{ .Values.namespace }}
-  labels:
-    {{- include "shorefront.labels" . | nindent 4 }}
-type: Opaque
-stringData:
-  POSTGRES_PASSWORD: {{ .Values.secrets.postgresPassword | quote }}
-  JWT_SECRET_KEY: {{ .Values.secrets.jwtSecretKey | quote }}