feat(mailer): support file attachments in sendMail()

Add optional `attachments` array to sendMail(), forwarded to both
Resend (base64-encoded content) and Nodemailer (pass-through).
Needed for emailNotif post-run emails in downstream projects.

Closes #3374

Author: PierreBrisorgueil

lib/helpers/mailer/tests/mailer.unit.tests.js

@@ -93,7 +93,7 @@ describe('mailer index with resend provider unit tests:', () => {
     );
   });
 
-    test('should return null on send error', async () => {
+  test('should return null on send error', async () => {
     mockSend.mockRejectedValue(new Error('API failure'));
 
     const result = await mailer.sendMail({