refine: required confirmation_email field on both student forms, StudentEmail uses it directly

- Add dedicated 'confirmation_email' (type=email, required) field
  to student form at end of submission (partage + admin).
- ThesisCreateController now validates it is present and a valid
  email; form is rejected if missing/invalid.
- Autofocus mapping for confirmation_email errors.
- StudentEmail uses confirmation_email directly (removed extractEmail
  hack that mined email from free-form contact field).

app/public/admin/acces-etudiante.php

@@ -83,6 +83,10 @@ $bodyClass = 'admin-body';
                     <td><?= $created ?></td>
                     <td>
                         <div class="admin-actions">
+                            <a href="/partage/<?= urlencode($link['slug']) ?>" target="_blank" rel="noopener"
+                               class="admin-btn-sm admin-btn-visit" title="Visiter le formulaire">
+                                👁 Visiter
+                            </a>
                             <button type="button" class="admin-btn-sm admin-btn-view"
                                     onclick="copyUrl(<?= $link['id'] ?>)" title="Copier l'URL">
                                 Copier