fix(logtail): keep mail.log in /data and reconcile stuck rows (v1.x closure phase 2)

Move the delivery log from the ephemeral /var/log to /data/log/mail.log so
the lines that resolve a queued send-log row survive a container recreate.
postlogd writes it as postfix, the panel reads it through the selfpost group
(dir 2750, file 0640, normalised every start); backups exclude log/.

Close the residual gap with a queue sweep: rows queued for over two minutes
whose id postqueue -p no longer lists are marked bounced. The sweep waits
until the tailer has read the log to its end and does nothing when the queue
cannot be listed, so a message in flight is never touched.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Co-authored-by: Cursor <cursoragent@cursor.com>

test/e2e/mail_helpers.go

@@ -74,7 +74,7 @@ var connectFromPattern = regexp.MustCompile(`connect from [^\[]*\[([0-9a-fA-F.:]
 // lastSMTPClientIP reads mail.log inside the selfpost container and returns
 // the most recent address Postfix's smtpd logged a connection from.
 func lastSMTPClientIP(s *stack) (string, error) {
-	out, err := s.execIn("selfpost", "tail", "-n", "200", "/var/log/mail.log")
+	out, err := s.execIn("selfpost", "tail", "-n", "200", "/data/log/mail.log")
 	if err != nil {
 		return "", err
 	}