fix: allow a pinned CI base-image mirror on Server

scripts/build-verify.sh

@@ -6,5 +6,9 @@ cd "$(dirname "$0")/.."
 DOCKER_BIN=${DOCKER_BIN:-docker}
 "$DOCKER_BIN" info >/dev/null
 "$DOCKER_BIN" compose config --quiet
-"$DOCKER_BIN" compose build --pull
+set -- --pull
+if [ -n "${CI_PYTHON_BASE:-}" ]; then
+  set -- "$@" --build-arg "PYTHON_BASE=$CI_PYTHON_BASE"
+fi
+"$DOCKER_BIN" compose build "$@"
 "$DOCKER_BIN" image inspect "${FRAME_FLOW_IMAGE:-pigway-frame-flow:latest}" --format 'image={{.Id}} size_bytes={{.Size}} architecture={{.Architecture}}'