Fix integration tests: allow plain-text auth in Stalwart dev config

Stalwart 0.14 disables PLAIN/LOGIN on non-TLS ports by default:
- [imap.auth] allow-plain-text = true  → unblocks IMAP LOGIN
- [session.auth] mechanisms + allow-plain-text → advertises PLAIN/LOGIN on SMTP

Also fix test: SMTP authenticates as "alice" not "alice@localhost"
(Stalwart SMTP auth accepts username without domain, unlike IMAP login)

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

stalwart-dev/config.toml

@@ -61,3 +61,12 @@ email  = ["bob@localhost"]
 [authentication.fallback-admin]
 user   = "admin"
 secret = "admin"
+
+# Allow LOGIN/PLAIN on the clear-text dev ports (no TLS in local test env).
+# By default Stalwart only advertises PLAIN/LOGIN when is_tls — override that.
+[imap.auth]
+allow-plain-text = true
+
+[session.auth]
+mechanisms = "[plain, login, oauthbearer, xoauth2]"
+allow-plain-text = true

test/integration/imap_sync_test.dart

@@ -63,7 +63,7 @@ void main() {
     final smtpClient = SmtpClient('test');
     await smtpClient.connectToServer(imapHost, smtpPort, isSecure: false);
     await smtpClient.ehlo();
-    await smtpClient.authenticate('$userA@localhost', passA);
+    await smtpClient.authenticate(userA, passA);
 
     final builder = MessageBuilder()
       ..from = [MailAddress('Alice', '$userA@localhost')]