fix: require TLS for IMAP auth, close port 143 (CERT-Bund compliance)

- Remove port 143 from mailserver (only expose 993/IMAPS)
- Enable SSL_TYPE=manual with Let's Encrypt certs
- Set DOVECOT_DISABLE_PLAINTEXT_AUTH=yes
- Add pentest_imap_tls config field (defaults to true)

Fixes CERT-Bund report: IMAP PLAIN/LOGIN without TLS on 46.225.100.82:143

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

compliance-agent/src/pentest/cleanup.rs

@@ -336,6 +336,7 @@ mod tests {
             pentest_verification_email: None,
             pentest_imap_host: None,
             pentest_imap_port: None,
+            pentest_imap_tls: true,
             pentest_imap_username: None,
             pentest_imap_password: None,
         }