Use CI variable for stage admin password

- Remove Secrets Manager config from values-stage.yaml
- Pass STAGE_ADMIN_PASSWORD via --set in deploy_stage
- Consistent with feature branch approach

Single source of truth: STAGE_ADMIN_PASSWORD CI variable is used by
deploy, reset, and integration test jobs.

.gitlab-ci.yml

@@ -430,6 +430,7 @@ deploy_stage:
         --namespace $NAMESPACE \
         -f $VALUES_FILE \
         --set image.tag=git.linux-amd64-$CI_COMMIT_SHA \
+        --set orchard.auth.adminPassword=$STAGE_ADMIN_PASSWORD \
         --wait \
         --atomic \
         --timeout 10m