feat(panel): give a delivery its history and its own log lines

The delivery page was a list of the fields the send-log table has no
column for, stacked one per line down the reading measure. Six values of
a few characters each — domain, application, queue id, journal id and two
timestamps — came to a page of mostly empty rows, and none of them
answered the question the log raises when a row is opened: what actually
happened to this message.

So the page states that instead. The subject heads it and the sender,
recipient and outcome are the line under it, which puts what the message
was and how it ended on the first line. Below, two columns: what the
journal recorded on the left, as a grid of tiles rather than a stack, and
on the right the two timestamps stated as the steps they stand for —
accepted and queued, then delivered, deferred, bounced, or refused before
queueing. Each step carries its status in the panel's own
ok/warn/error/unknown vocabulary, so a colour means here what it means on
the status page. A message still queued shows the report it is waiting
for as a step that has not happened, rather than dating it with the
moment the row was written.

Under both, at full width, the mail.log lines for the message's queue id.
The queue id was printed on this page as something to go and search the
system log for by hand; logtail.QueueLines does that search. It scans a
bounded tail of the current file — finding one message's lines means
reading rather than seeking — and anchors the match on the character
before the id, since queue ids are hexadecimal runs and a shorter one is
regularly the tail of a longer one. Send-log rows outlive mail.log
(retention ninety days, rotation fourteen files), so a message with
nothing left to show says so; that is the normal end state, not a fault,
and only a log that cannot be read at all is reported as one.

Two cards abreast and a block of raw log lines do not fit the reading
measure, so the page now declares itself wide — the opposite of what it
did when the column width was unified, where it was the page that stayed
prose. The mechanism is unchanged and is why the reversal costs one line:
how wide a page needs to be is the page's own property, not the
navigation entry's.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/architecture.md

@@ -121,6 +121,16 @@ replay a pre-existing log.
 Possible follow-ups if this becomes painful: mount the mail log under `/data`, or
 reconcile stuck rows via `postqueue`.
 
+**Two one-shot reads** sit beside the follow loop and are unrelated to it, both
+serving panel pages on request: `TailLines` (the last *n* lines, for
+`/system-log`) and `QueueLines` (the lines carrying one queue-id, for
+`/deliveries/{id}`). `QueueLines` scans a bounded tail of the current file —
+finding a message's lines means reading rather than seeking — and matches the id
+anchored on the character before it, since queue ids are hexadecimal runs and a
+shorter one is regularly the tail of a longer one. Send-log rows outlive the log
+(retention 90 days, rotation 14 files), so an empty result is the expected end
+state for an older message and the page reports it as such, not as a failure.
+
 ---
 
 ## Panel HTTP surface
@@ -136,7 +146,7 @@ unless noted.
 | `/status` | Process, cert, socket, PTR checks; machine CPU/memory/network |
 | `/domains`, `/domains/*` | Domain and application CRUD, DKIM, L2 limits |
 | `/deliveries` | Send log with filters |
-| `/deliveries/{id}` | One send-log row in full |
+| `/deliveries/{id}` | One send-log row in full, with its `mail.log` lines |
 | `/mail-queue` | Postfix queue view |
 | `/system-log` | `mail.log` tail |
 | `/reload` | Reload OpenDKIM + Postfix maps |