Umami: Align pnpm with engines.pnpm on update (#17404)

Umami 3.4.0 pins engines.pnpm to 12.3.4. update_script() never
refreshed pnpm, so containers installed with pnpm < 12 fail at
pnpm install with ERR_PNPM_UNSUPPORTED_ENGINE after the service was
already stopped and the old release replaced.

Read engines.pnpm from the deployed package.json and pass it to
setup_nodejs (same approach as ct/seerr.sh), falling back to latest.

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

ct/umami.sh

@@ -40,6 +40,9 @@ function update_script() {
     CLEAN_INSTALL=1 fetch_and_deploy_gh_release "umami" "umami-software/umami" "tarball"
     restore_backup
 
+    PNPM_VERSION=$(jq -r '.engines.pnpm // "latest"' /opt/umami/package.json)
+    NODE_VERSION="22" NODE_MODULE="pnpm@${PNPM_VERSION}" setup_nodejs
+
     msg_info "Updating Umami"
     cd /opt/umami
     $STD pnpm install