number_format() in PHP 8.3 strictly requires int|float; $wpdb->get_var()
returns string|null. Cast $total to (int) at point of assignment in
admin/partials/articles-list.php to fix HTTP 500 on Articles admin page.
Also add PHPUnit test covering the string->int cast contract.
Fixes#31. Version bump 2.5.0 -> 2.5.1.
Agent-Session: fix-articles-500-20260617