install_user_manager appended a 'Match User' block to sshd_config with no
marker guard, unlike the rootless .bashrc block beside it. The enclosing
'if ! userExists' gate hides it today, but a user delete+recreate would append
a second block. Guard on the '### LibrePortal Manager User Start' marker so the
append is idempotent.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Signed-off-by: librelad <librelad@digitalangels.vip>
ba385a8b97