fix: resolve broken lib/ require paths in admin and normalise modern-normalize to .min.css

public/admin/add.php

@@ -1,7 +1,7 @@
 <?php
 // Bootstrap application
 require_once __DIR__ . "/../../config/bootstrap.php";
-require_once __DIR__ . '/../../lib/AdminAuth.php';
+require_once __DIR__ . '/../../src/AdminAuth.php';
 
 // PHP-level auth guard (defence-in-depth behind nginx Basic Auth)
 AdminAuth::requireLogin();
@@ -13,7 +13,7 @@ if (empty($_SESSION["csrf_token"])) {
 $pageTitle = "Ajout de TFE";
 
 // Load database helper
-require_once __DIR__ . '/../../lib/Database.php';
+require_once __DIR__ . '/../../src/Database.php';
 
 try {
     $db = new Database();