fix(build): build the loki/alloy/comfyui images in docker format

The healthcheck added to the loki image was discarded by the build:
'HEALTHCHECK is not supported for OCI image format and will be ignored'.
podman builds OCI by default, and OCI has no HEALTHCHECK field, so the
container came back with no health at all — worse than the failing check it
replaced, because nothing reports the loss.

The build now passes --format docker, and the seam pins it so a future edit
cannot quietly reintroduce an image with no health field.

tests/observability_quadlet.bats

@@ -161,6 +161,13 @@ service_section() {
     grep -q 'COPY --from=tools /bin/busybox.static /usr/local/bin/busybox' "$cf"
 }
 
+@test "the loki/alloy/comfyui build uses the docker image format" {
+    # Without --format docker the loki healthcheck is silently discarded (OCI
+    # has no HEALTHCHECK field) and the container stops reporting health.
+    grep -q -- '--format docker' "$REMOTE_DEPLOY"
+    grep -q 'podman build --format docker --no-cache' "$REMOTE_DEPLOY"
+}
+
 @test "grafana gets its OAuth client secret without getting a whole env file" {
     # systemd expands ${GRAFANA_OAUTH_CLIENT_SECRET} for the [Container]
     # Environment= line from the [Service] EnvironmentFile, which keeps the