delivery-log-storage: a message's page reads its stored lines

The Delivery log box on a message's page was filled by searching the current
mail.log on every view; that file is rotated daily, so the box was empty for
anything not sent today. deliveryLog now asks the store for the row's lines -
its queue id, dated within the row's queue lifetime plus a day
(RetryPolicy.LongestLifetime) - and shows the latest 200, oldest first.

When nothing is stored the page still searches the current file, which is
what shows a message accepted before 2.2.0. When that finds nothing either,
the note no longer blames rotation for the ordinary case: it says lines are
kept with the row since 2.2.0. The Outbound log help topic in help.go follows
the mockup changed in fc184ec, word for word.

Checked on Windows: go vet clean; go test ./internal/web/... ./internal/postfix
./internal/store pass, the guards among them. New test: lines shown from the
table when mail.log holds none of them, without another queue id's lines and
without those of an earlier message under the same id.

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

internal/web/view/help.go

@@ -162,7 +162,7 @@ var outboundTopics = []HelpTopic{
 	}},
 	{ID: HelpLog, Title: "Outbound log", Body: []Text{
 		Rich("One row per message and recipient, with the status Postfix last reported: queued (accepted, nothing reported yet), sent (the receiving server took it; what the mailbox does next is not reported back), deferred (not taken yet, Postfix tries again), bounced (failed for good, or the queue lifetime ran out) and rejected (refused before queueing under a level-2 rate limit, so it never reached Postfix). A message's page lists these steps and the lines Postfix wrote about it in ",
-			Code("mail.log"), ", found by queue id; that file is rotated daily and about two weeks are kept, so an old message may show none. Rows are deleted after the retention set in Server › Settings, 90 days by default. A domain administrator sees only the rows of their own domains."),
+			Code("mail.log"), ", found by queue id. The lines are kept with the row: they stay on the page after that file has rotated, for as long as the row does. A message accepted before version 2.2.0 shows them only while they are still in the current file. Rows are deleted after the retention set in Server › Settings, 90 days by default, and their lines with them. A domain administrator sees only the rows of their own domains."),
 	}},
 	{ID: HelpQueue, Title: "Queue and retries", Body: []Text{
 		Rich("The page lists, as ", Code("postqueue -p"), " prints it, the messages Postfix has accepted and not yet delivered: mail being sent right now and mail deferred for a later attempt. Only the global role can open it, and it only shows; nothing here deletes or forces a message. A deferred message is tried again after the first retry delay, then at gaps that double up to a cap, until the receiving server takes it or the queue lifetime runs out and it bounces; there is no attempt counter, and the box on the page shows this server's values. A queue that keeps growing means a receiver is refusing or not answering: open the message from the Outbound log to read the reason Postfix logged."),

internal/web/view/outbound_log.go

@@ -189,7 +189,7 @@ type OutMessage struct {
 	Delivery Box
 	LogLines []LogLine
 	// LogEmpty says why there are no lines: a message that never reached the
-	// queue, or whose lines have been rotated away, is an ordinary outcome.
+	// queue, or that predates the stored lines, is an ordinary outcome.
 	LogEmpty EmptyState
 }