Integrate G15 submodules with Debian 13 packaging and devcontainer

packaging/container-build.sh

@@ -0,0 +1,7 @@
+#!/bin/bash
+set -euo pipefail
+# This entry point installs packages: use only in a disposable container.
+[[ -f /.dockerenv && $EUID == 0 ]] || { echo 'Disposable root Docker container required' >&2; exit 1; }
+apt-get update
+bash packaging/build.sh /out
+bash packaging/test.sh /out