K-114: SSH root login prompt with sshd drop-in in the install path

prompt_lxc_config asks 'SSH-Root-Login erlauben? [Y/n]' (env-presettable
via SSH_ROOT_LOGIN, validated, normalized to yes|no). The bootstrap passes
the value into the container; configure_ssh_root_login writes
/etc/ssh/sshd_config.d/zz-root-login.conf (yes -> PermitRootLogin yes,
no -> prohibit-password) and reloads sshd.

install/nexus-db-install.sh

@@ -36,6 +36,7 @@ CRED_FILE="/root/nexus-db.credentials"
 
 # ── packages: PGDG repo + PostgreSQL 16 + pgvector ────────────────────────────
 setup_base_apt curl ca-certificates gnupg lsb-release
+configure_ssh_root_login
 
 if [[ ! -f /etc/apt/sources.list.d/pgdg.sources ]] && [[ ! -f /etc/apt/sources.list.d/pgdg.list ]]; then
   msg_info "Adding PGDG apt repo..."