feat: email retry page on 550 rejection; confirmation_email optional in admin form

app/src/StudentEmail.php

@@ -102,9 +102,8 @@ class StudentEmail {
         try {
             $result = SmtpRelay::send($db, $to, $subject, $htmlBody);
         } catch (SmtpSendException $e) {
-            // Confirmation email failure must not abort the successful submission.
             error_log("[StudentEmail] SMTP error sending to {$to} for thesis #{$thesisId}: " . $e->getMessage());
-            return false;
+            throw $e;  // re-throw so callers can react (e.g. redirect to retry page)
         }
 
         if ($result) {