docs: stage 1 of the audit - log tailer, reconcile, sender check, guide

architecture.md
- § Log tailer: the rotation drain does not close the gap entirely
  (postlogd writes to the renamed file until the reload reaches it); the fix
  waits for the measurement. Delivery lines read at the head of the line
  (M12).
- § Queue reconcile: reason "reconcile", the 4 MiB cap, the conditional
  close; the measurement (delivery_log_days, its four counters) and the
  decision rule written before the data.
- § Sender check, what it costs: cleanup meets a check that hangs mid-message,
  with the warning seen on the stand; counted once per message.

guide.md
- § Outbound log: `bounced` is the panel's word when Postfix no longer holds
  a message and the log never said; it is counted.
- § Overview and Health, Sender check: the message a hung panel deferred is
  counted too.

Audit plan line ticked, roadmap 14/61. Stage 1's code items are done
(the two deferred tailer fixes wait for the data, as planned).

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

docs/guide.md

@@ -410,7 +410,8 @@ readings, in the order of what stops mail first:
   not counted: mail was stopped for another reason then. What is counted as
   a message is a connection Postfix turned away - it refuses before a
   message is offered - so a monitor that only connects during an outage is
-  counted too. Days are UTC days. The card warns when
+  counted too; and when the panel hangs instead of stopping, the message it
+  hung on. Days are UTC days. The card warns when
   a message was deferred in the last 24 hours. If these numbers do not stay
   at nothing, the panel is in the way of your mail more than it should be -
   report it.
@@ -1257,7 +1258,12 @@ rows of their domains. It refreshes its rows without resetting a filter being
 chosen. A row identifies its message and nothing more — time,
 sender, recipient, subject and status `queued` (accepted, not yet
 delivered), `sent` (handed off successfully), `deferred` (Postfix is
-retrying), `bounced` (final failure), or refused before it was queued. A
+retrying), `bounced` (final failure), or refused before it was queued.
+`bounced` is usually Postfix's word; it is the panel's when Postfix no longer
+holds a message and `mail.log` never said what became of it (the log rotated
+away while the panel was down, or was not readable) - the panel then closes
+the row as a failure rather than show a delivery it cannot evidence, and
+counts that it did. A
 refused row says why in its tag: `rate-limited` (a [level-2 rate
 limit](#rate-limiting--level-2-domain-and-application)), `wrong client` (the
 application's client IP list) or `wrong From` (see [Who an application may