pivot to a systemd unit for the online hook

serving/.env.example

@@ -1,7 +1,7 @@
 # Copy to .env and edit for your test LAN/bridge, then: docker compose up -d
 
 # Release being served. Must match the Packer build (fleet-<version>.efi).
-IMAGE_VERSION=0.0.0-a508dce
+IMAGE_VERSION=0.0.0-2eefd97
 
 # OCI release-artifact image (built by scripts/build-oci.sh). Mounted directly
 # as a Docker image volume — the default artifact source. Pin by digest in
@@ -10,7 +10,7 @@ OCI_IMAGE=git.bitasylum.org/audiobuzz/fleet-boot
 
 # Fallback only (Docker < 28 / offline): local Packer output dir, used by the
 # commented bind-mounts in docker-compose.yml. Ignored when image volumes work.
-ARTIFACT_SRC=../artifacts/0.0.0-a508dce
+ARTIFACT_SRC=../artifacts/0.0.0-2eefd97
 
 # SPDK NVMe/TCP target image — prebuilt + pushed by CI
 # (.gitea/workflows/spdk-image.yaml); the serving host just pulls it.