Add Makefile and bin/ scripts for one-command multi-arch release

make release builds, smoke-tests and pushes amd64 (on fsn1app1 via
DOCKER_HOST) and arm64 (local), joins them into latest and dated
multi-arch manifests, and commits the day's logs. Logic lives in bin/;
the Makefile only wires dependencies so -j2 runs the arches in parallel.

bin/clean

@@ -0,0 +1,10 @@
+#!/usr/bin/env bash
+# Remove dev-tagged images from every arch's daemon.
+set -euo pipefail
+cd "$(dirname "$0")/.."
+. bin/lib.sh
+
+for arch in ${ARCHES:-amd64 arm64}; do
+    use_arch_host "$arch" || continue
+    docker rmi -f "$(dev_tag "$arch")" 2>/dev/null || true
+done