audit 4: findings of the two reviews

- Two inbound domains on one upstream could never change its TLS mode,
  each save refused for the other (medium): SetTransportAs changes the
  mode for every domain on the upstream when the one saving may change
  them all; a domain user who may not is refused with the mode, not the
  other tenant's domain name (security F1: the first version named it).
- A deletion's leftover DKIM key is removed by Resync (Reload
  configuration, a restore's first start) for names no domain has.
- The backup's write deadline moves before Check.
- hasUnsavedEdit skips password and file fields and compares a multiple
  select's options; htmx.config.timeout 30 s, so a refresh never answered
  ends and is tried again; a failed refresh's promise is handled.
- An empty filtered Outbound log says no message matches the filters.
- The dummy bcrypt hash is made at start; a DMARC part over 8 MiB is
  refused for its size like the other two limits.
- Health's Configuration box says what Reload writes (design first,
  32dfe4a).
- Docs: CHANGELOG, guide § Inbound, security.md (the shared upstream's
  mode, the profile form's "username taken"), architecture.md (owed to an
  address), the plan's notes corrected.
Tests: the shared upstream (service, handler), the leftover key, all eight
Health boxes ordered, the subject from before migration 0011, the new JS
cases.

Tested on the test server: go vet + go test of 25 packages, make e2e (all
pass, 636 s) on this tree.

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

docs/architecture.md

@@ -401,7 +401,10 @@ is sent; the operator's view is guide § Notifications.
   who are still recipients. A user who comes to hear of a subject only while
   it is open is not mailed about it, and its ending goes to those who were
   told. A subject opened before `2.5.4` has no such record, and its ending
-  goes to every recipient, as it did.
+  goes to every recipient, as it did. It is owed to an address: a user who
+  changes their e-mail while a subject is open is a new address, told
+  neither its follow-up nor its end - accepted, a subject lasts hours to
+  days.
 - **The notifier's own mail is not a subject.** A notification waiting for a
   mailbox that does not answer, or its bounce coming back to
   `postmaster@<hostname>` - which receives no mail - is left out of the