feat(pkg): debconf prompt for initial AuthForge policy on metapackage install

debian/authforge.config

@@ -0,0 +1,14 @@
+#!/bin/sh
+# Asks the admin for an initial policy. Postinst (Task 6) reads the
+# answer and writes /etc/authforge/policy.d/00-debconf.conf on first
+# install only. Re-runs (e.g. `dpkg-reconfigure authforge`) re-prompt
+# but do not overwrite an existing seed file unless the admin chose to.
+set -e
+
+# shellcheck source=/dev/null
+. /usr/share/debconf/confmodule
+
+db_input medium authforge/initial-policy || true
+db_go || true
+
+exit 0