design: the Outbound log help topic says the lines are kept

The topic said a message's lines are found in mail.log by queue id and that an
old message may show none, because that file is rotated. With
delivery-log-storage the lines are kept with the row: they stay on the page
for as long as the row does and go with it. A message accepted before 2.2.0
shows them only while they are in the current file.

Mockup source and its built page only; help.go follows with the page.
build.py: 35 pages; check.py: 32 screens, 52 sp- classes, 0 violations.

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

docs/plans/delivery-log-storage.md

@@ -144,7 +144,7 @@ Target version cut: **`2.2.0`** (MINOR). One commit per step;
 
 - [x] Migration `0003_send_log_lines.sql`, store methods (insert, insert once, lines of a row, prune) and their tests — **Opus**
 - [x] Log tailer: store queue-id lines, write once while catching up, prune with the send-log sweep and hourly — **Opus**
-- [ ] The two texts, mockup first: the *Outbound log* help topic and the empty note (`design:` commit) — **Opus**
+- [x] The two texts, mockup first: the *Outbound log* help topic and the empty note (`design:` commit) — **Opus** (the help topic is in the mockups; the empty note is not drawn there - the `out-message` mockup shows a message with lines - and changes with the page)
 - [ ] Message page reads the table, falls back to the current `mail.log`; help text in `help.go` — **Opus**
 - [ ] [architecture.md](../architecture.md), [guide.md](../guide.md), [schema-migrations.md](../schema-migrations.md) — **Opus**
 - [ ] `go vet`, `go test`, e2e: a message's page still lists its lines after a forced rotation — **Opus**