fix(smtp): reject the relay when the outgoing server cannot be reached

SMTPConnection only calls the connect() callback once the handshake
succeeds; a refused or timed out connection is emitted as an 'error'
event, which was only logged. relay() then never settled, so its finally
block (which now releases the email stream) never ran, auto-relay held
the incoming SMTP transaction open without a reply, and the REST relay
request hung. Reject the connect promise from the 'error' handler.

.changeset/fix-relay-connect-error.md

@@ -0,0 +1,9 @@
+---
+'@maildev/smtp': patch
+'maildev': patch
+---
+
+Fail the relay when the outgoing server cannot be reached. The connection
+error was only logged, so the relay never finished: with auto-relay on, the
+SMTP client sending to MailDev never got its reply, and the manual relay
+request never answered.