panel-notifications: guide, architecture, security; refusals looked for every minute

guide.md gains Notifications: the four things, when each is said and said
again, who is told, the two switches, and the two DNS records of the server's
own name that make the mail arrive. architecture.md: the notifier as the
fifth role, its readings, state, recipients and sending; the server's own key
in OpenDKIM's tables; non_smtpd_milters. security.md: the panel submits mail
of its own - how, to whom, and what text from outside can reach a body.

That text - a queued message's sender, a DNS finding - is reduced to
printable ASCII and cut before it is printed. Refused mail is looked for
every minute instead of every five: it is one indexed query, and a refusal is
mail not being sent now. The image's note on the panel's postdrop membership
no longer calls it read-side only.

go test ./internal/notify passes.

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

internal/notify/notify.go

@@ -29,8 +29,9 @@ const (
 	// at. A var-free constant: the rules below count in checks.
 	CheckInterval = time.Hour
 	// LimitInterval is how often refused mail is looked for. A refusal is
-	// reported at once rather than on the hour: it is mail not being sent now.
-	LimitInterval = 5 * time.Minute
+	// reported within the minute rather than on the hour: it is mail not being
+	// sent now. The look is one indexed query.
+	LimitInterval = time.Minute
 
 	// dnsChecks is how many checks in a row must agree before a DNS mismatch is
 	// reported, and before it is reported gone. One check is a resolver's bad