Add isolated Debian installer with credential setup and guarded updates

install.sh

@@ -0,0 +1,8 @@
+#!/usr/bin/env bash
+set -euo pipefail
+SCRIPT_DIR="$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" && pwd)"
+if ! command -v python3 >/dev/null 2>&1; then
+  echo 'Python 3 fehlt. Auf einem frischen Debian zuerst: sudo apt-get install python3' >&2
+  exit 1
+fi
+exec python3 "$SCRIPT_DIR/deploy/install.py" "$@"