feat: student mode support for thanks page (admin-auth only)

- add hidden student_mode field in add.php form
- pass mode=student through redirect to thanks.php in formulaire.php
- thanks.php renders clean student thank-you page (no header, centered button)
- add CSS for .thanks-student-page, .btn-new-form, .thanks-success, .thanks-error
- admin auth always required; student mode is purely UI variant on the physical machine

public/admin/thanks.php

@@ -3,14 +3,16 @@
 require_once __DIR__ . "/../../config/bootstrap.php";
 require_once __DIR__ . '/../../src/AdminAuth.php';
 
-// PHP-level auth guard (defence-in-depth behind nginx Basic Auth)
-AdminAuth::requireLogin();
-
 // Configure error reporting
 ini_set('display_errors', 0);
 ini_set('log_errors', 1);
 ini_set('error_log', 'error.log');
 
+$studentMode = isset($_GET['mode']) && $_GET['mode'] === 'student';
+if (!$studentMode) {
+    AdminAuth::requireLogin();
+}
+
 require_once __DIR__ . '/../../src/Database.php';
 
 // Security: Validate thesis ID parameter
@@ -62,10 +64,48 @@ function formatFileSize($bytes) {
 // Set page title for header
 $pageTitle = "Récapitulatif TFE";
 ?>
-<?php $isAdmin = true; $bodyClass = 'admin-body'; require_once APP_ROOT . '/templates/head.php'; ?>
-    <?php include APP_ROOT . '/templates/header.php'; ?>
+<?php
+$isAdmin = true;
+if ($studentMode) {
+    $bodyClass = 'admin-body student-body';
+    require_once APP_ROOT . '/templates/head.php';
+} else {
+    $bodyClass = 'admin-body';
+    require_once APP_ROOT . '/templates/head.php';
+    include APP_ROOT . '/templates/header.php';
+}
+?>
 
 <main id="main-content">
+    <?php if ($studentMode): ?>
+    <!-- ═══════════════════ STUDENT MODE: Thank you page ═══════════════════ -->
+    <div class="thanks-student-page">
+        <?php if ($error): ?>
+            <div class="thanks-error">
+                <h1>⚠ Oups…</h1>
+                <p><?= htmlspecialchars($error) ?></p>
+                <a href="/admin/add.php?mode=student" class="btn-new-form">← Retour au formulaire</a>
+            </div>
+
+        <?php elseif ($thesis): ?>
+            <div class="thanks-success">
+                <h1>Merci 🎉</h1>
+                <p class="thanks-message">
+                    Ton TFE <strong><?= htmlspecialchars($thesis['title']) ?></strong> a bien été soumis.
+                </p>
+                <a href="/admin/add.php?mode=student" class="btn-new-form">+ Ajouter un nouveau TFE</a>
+            </div>
+        <?php else: ?>
+            <div class="thanks-error">
+                <h1>Erreur</h1>
+                <p>Aucune donnée à afficher.</p>
+                <a href="/admin/add.php?mode=student" class="btn-new-form">← Retour au formulaire</a>
+            </div>
+        <?php endif; ?>
+    </div>
+
+    <?php else: ?>
+    <!-- ═══════════════════ ADMIN MODE: Recap page ═══════════════════ -->
     <h1>Récapitulatif TFE</h1>
 
     <?php if ($error): ?>
@@ -148,6 +188,8 @@ $pageTitle = "Récapitulatif TFE";
         <p class="admin-muted">Aucune donnée à afficher.</p>
         <p><a href="/admin/add.php" class="admin-btn-secondary">Retour au formulaire</a></p>
     <?php endif; ?>
+
+    <?php endif; ?>
 </main>
 
 <?php require_once APP_ROOT . '/templates/admin/footer.php'; ?>