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/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
 }