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.

dankclaw/loki/Containerfile

@@ -10,7 +10,12 @@
 # container report its own health instead of looking merely "Up" while wedged.
 #
 # Build on dankclaw:
-#   podman build -t franksdank/loki:latest -f dankclaw/loki/Containerfile .
+#   podman build --format docker -t franksdank/loki:latest \
+#       -f dankclaw/loki/Containerfile .
+#
+# --format docker is required: podman's default OCI image format has no
+# HEALTHCHECK field, so a default-format build warns and silently discards the
+# one below, leaving a container that reports no health at all.
 
 FROM docker.io/library/alpine:latest AS tools
 # busybox-static is statically linked: the target images have no dynamic