fix: skip external MariaDB repo on trixie, clean stale repo files

- Trixie uses native Debian mariadb packages (external repo has no
  trixie release), so wo_mysql_repo is empty and repo add is skipped
- Clean up old openlitespeed.list and mariadb.list during install so
  they get regenerated with correct GPG keyring paths

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

install

@@ -859,6 +859,10 @@ wo_init_variables
 _run wo_clean_repo
 _run wo_download_gpg_keys
 
+# clean up stale repo list files so they get regenerated correctly
+rm -f /etc/apt/sources.list.d/openlitespeed.list 2>/dev/null
+rm -f /etc/apt/sources.list.d/mariadb.list 2>/dev/null
+
 if [ -z "$wo_force_install" ]; then
     # check distribution support
     wo_check_distro