review: clear stale attribution, gate numberless PUTs, cite the ADR

A Poll finding a higher number now clears series.latest_raised_by: the value
it stores is its own, so the next Poll must not credit that Reader with an
agreement they did not earn, nor charge them for a retraction of a number
they never reported.

A PUT carrying no chapter is no Sighting and defers nothing. The ceiling now
counts the Site's own rest rather than defaultRest. The userscripts PUT an
unchanged read too - the case the whole mechanism exists for was the one they
never sent.

ADR-0011 carries its citations and states honestly when a Reader's marks take
effect.

backend/internal/latest/sites.go

@@ -409,13 +409,14 @@ const (
 	// asleep (ADR-0005 on-demand browser).
 	browserWakeCount = 5
 	browserWakeAge   = 15 * time.Minute
-	// sightingCeiling caps Sighting deferral (issue #103): however many
-	// Sightings arrive, a Series unpolled for this long is Polled. It is what
-	// makes a client report safe to trust — a wrong Latest Chapter dies within
-	// the ceiling deterministically, rather than in expectation the way a
-	// randomised audit would have it. Six rests, so a Series a Reader visits
-	// constantly still gets one authoritative check per working day-part.
-	sightingCeiling = 6 * defaultRest
+	// sightingCeilingRests caps Sighting deferral (issue #103): however many
+	// Sightings arrive, a Series unpolled for this many of its Site's rests is
+	// Polled. It is what makes a client report safe to trust — a wrong Latest
+	// Chapter dies within the ceiling deterministically, rather than in
+	// expectation the way a randomised audit would have it. Six, so a Series a
+	// Reader visits constantly still gets one authoritative check per working
+	// day-part.
+	sightingCeilingRests = 6
 )
 
 // effectiveGap is a Site's pace: the registry gap, or one rest divided by the