fix: an asleep browser Lane is not a stalled one on the admin page

laneRow.Stalled was Due > 0 && Checked == 0, which is exactly the shape
of the on-demand wake gate declining to start Chrome (ADR-0005): under
five due Series and none overdue by 15m, a browser Lane reads nothing on
purpose. kagane and novelfull each have one bookmarked Series, so that is
their state for most of every cycle and the page marked both "not
checking" — spending the one mark that means "go look" on the commonest
healthy state.

LaneState.Asleep is set at the wake gate, excluded from Stalled, kept out
of Attention, and rendered as "browser asleep". Verified in prod: those
Lanes wake on the age rule 15m past due (kagane and novelfull both polled
at 14:55Z for a 14:40Z due moment, novelfull picking up Chapter 4458).

backend/internal/latest/status.go

@@ -19,6 +19,11 @@ type LaneState struct {
 	Clamped  bool
 	Refusing bool
 	Browser  bool
+	// Asleep marks a browser Lane whose last pass declined to wake Chrome
+	// because it was under both wake thresholds (ADR-0005). Due without
+	// Checked then means "waiting for the group to gather", not "stopped", and
+	// the page must not draw it as a stall.
+	Asleep bool
 }
 
 // Status is the owner's page snapshot of the whole poller (issue #102).