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>

internal/postfix/queue.go

@@ -3,6 +3,7 @@ package postfix
 import (
 	"fmt"
 	"os/exec"
+	"regexp"
 	"strings"
 )
 
@@ -20,3 +21,43 @@ func Queue() (string, error) {
 	}
 	return string(out), nil
 }
+
+// QueueIDs returns the set of queue ids Postfix is still holding — everything
+// in the maildrop, incoming, active, deferred and hold queues. It answers the
+// one question the log-tailer's reconcile sweep asks about a send-log row stuck
+// at "queued": is Postfix still working on this message, or has it left the
+// queue without the panel ever seeing a delivery line for it (architecture.md §
+// Log tailer)?
+//
+// An error means the queue could not be listed and therefore says nothing about
+// any message; the caller must treat it as "no information", never as an empty
+// queue.
+func QueueIDs() (map[string]struct{}, error) {
+	out, err := Queue()
+	if err != nil {
+		return nil, err
+	}
+	return parseQueueIDs(out), nil
+}
+
+// queueEntryRe matches the first line of a `postqueue -p` entry, e.g.
+//
+//	3C5B04E6C1*     446 Thu Aug  7 10:12:31  app@example.com
+//
+// The id is at the start of the line, optionally flagged '*' (in the active
+// queue) or '!' (on hold), and is followed by the message size. Requiring the
+// size is what separates an entry from the listing's other left-margin lines:
+// the '-Queue ID-' header, the '-- 5 Kbytes in 2 Requests.' trailer, a deferred
+// entry's '(connect timed out)' reason, and 'Mail queue is empty'. Recipient
+// lines are indented and never match.
+var queueEntryRe = regexp.MustCompile(`^([0-9A-Za-z]+)[*!]?\s+\d+\s`)
+
+func parseQueueIDs(listing string) map[string]struct{} {
+	ids := make(map[string]struct{})
+	for _, line := range strings.Split(listing, "\n") {
+		if m := queueEntryRe.FindStringSubmatch(line); m != nil {
+			ids[m[1]] = struct{}{}
+		}
+	}
+	return ids
+}