fix(tui): default SMTP port to 465 in the account form

NewAccountForm prefilled defaults for mode, IMAP port, and both securities but
left SMTP port blank. Default it to 465 to match `account add --smtp-port`.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/tui/account.go

@@ -203,6 +203,9 @@ func NewAccountForm(initial Fields, editing bool) AccountForm {
 	if initial.IMAPSecurity == "" {
 		initial.IMAPSecurity = "tls"
 	}
+	if initial.SMTPPort == "" {
+		initial.SMTPPort = "465"
+	}
 	if initial.SMTPSecurity == "" {
 		initial.SMTPSecurity = "tls"
 	}