fix: email mask shows max 4 chars instead of half the local part

lizandro.guarnizo (17 chars) was showing 'lizandro.' (9 chars including the dot)
because ceil(17/2)=9. Now always shows exactly min(4, len) chars: 'liza*************@domain'

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/Services/TelegramBotService.php

@@ -1366,8 +1366,8 @@ class TelegramBotService
     {
         [$local, $domain] = explode('@', $email, 2);
         $len     = mb_strlen($local);
-        $visible = max(4, (int) ceil($len / 2)); // muestra la mitad, mínimo 4 caracteres
-        return mb_substr($local, 0, min($visible, $len)) . str_repeat('*', max(0, $len - $visible)) . '@' . $domain;
+        $visible = min(4, $len); // siempre 4 caracteres máximo
+        return mb_substr($local, 0, $visible) . str_repeat('*', max(0, $len - $visible)) . '@' . $domain;
     }
 
     private function createMPPreference(string $titulo, int $valor, string $ref): ?string