delivery-log-storage: e2e holds the page to its lines after a rotation

New step delivery_log_survives_rotation: the page of the first delivered
message must list the line that opened its queue id and its delivery line,
then mail.log is rotated with logrotate -f, the current file is checked to
hold no delivery line, and the page must list both lines still. Before this
feature the page searched the current file and would show none.

The step runs after negative_level1_ratelimit: placed right after the first
delivery it rotated away the "connect from" line the level-2 step reads from
the current log, and that step failed.

On the test server, for this tree: go vet clean, go test ./... 22 packages
ok, make e2e ok (126 s).

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

docs/plans/delivery-log-storage.md

@@ -147,6 +147,6 @@ Target version cut: **`2.2.0`** (MINOR). One commit per step;
 - [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)
 - [x] Message page reads the table, falls back to the current `mail.log`; help text in `help.go` — **Opus**
 - [x] [architecture.md](../architecture.md), [guide.md](../guide.md), [schema-migrations.md](../schema-migrations.md) — **Opus** (schema-migrations.md went in with the migration)
-- [ ] `go vet`, `go test`, e2e: a message's page still lists its lines after a forced rotation — **Opus**
+- [x] `go vet`, `go test`, e2e: a message's page still lists its lines after a forced rotation — **Opus** (on the test server: vet ok, 22 packages ok, e2e ok with the new step `delivery_log_survives_rotation`)
 - [ ] Technical review — **Opus**
 - [ ] Security review — **Fable**