logtail: the sweep closes only queued rows, with reason "reconcile" (audit H3)

reconcile() closed a row through UpdateStatus (WHERE queue_id AND to_addr),
which could overwrite a "sent" the tailer wrote between the listing and the
close, and rewrite an old row of a reused queue id. store.CloseUnreported
sets status bounced and reason "reconcile" (store.ReasonReconcile; the
0006 column, no schema change) WHERE ... AND status = 'queued'; the sweep
counts rows actually closed.

Tests: store - a queued row is closed with the reason, a sent row is left
alone (0 rows); logtail - the sweep's close goes through CloseUnreported.

CHANGELOG [Unreleased], audit plan line ticked, roadmap 9/61.
Evidence: go vet ./... clean; go test ./internal/store ok, ./internal/logtail
ok but for TestFollowTailsAndRotates (Windows rename of an open file, fails
here always); the server run of the stage follows before the push.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/store/sendercheck.go

@@ -13,6 +13,10 @@ const (
 	ReasonFrom   = "from"   // the From: line is not the application's
 )
 
+// ReasonReconcile marks a "bounced" row the reconcile sweep closed (send_log.reason):
+// its message left Postfix's queue with no delivery line ever read for it.
+const ReasonReconcile = "reconcile"
+
 // Settings keys of the sender check's statistics.
 const (
 	// settingSenderCheckSince is the first UTC day the statistics cover.