feat(web): read admin lanes from the durable pass log, not a poller snapshot (#145)

The Lanes page now projects store.LatestLanePasses and the owner-window
outcomes (store.LanePassOutcomes) into per-Site rows instead of reading an
in-memory Poller snapshot, so a deploy answers the instant the store is up.
Browser configuration is a config fact and reachability is derived from
recent browser-Site passes inside latest.RefuseBackoff.

This atomically deletes the in-memory path in the same commit that makes the
page read the DB: latest/status.go (LaneState, Status, LaneStatus,
recordLaneState) and the web.LaneReporter seam plus fakeLanes are gone, and
latest.refuseBackoff is renamed latest.RefuseBackoff at every callsite.
ownerWindow (#142) is referenced, never declared (contract C2)

backend/internal/latest/sites.go

@@ -401,9 +401,10 @@ const (
 	// express (docs/research/cloudflare-bot-scoring-and-poll-cadence.md);
 	// below it the Lane is outrunning its own plan and says so loudly.
 	minGap = time.Second
-	// refuseBackoff is how long a Lane waits after its Site refused twice in
-	// one run before attempting it again.
-	refuseBackoff = 15 * time.Minute
+	// RefuseBackoff is how long a Lane waits after its Site refused twice in
+	// one run before attempting it again. Exported so the web layer can derive
+	// browser reachability from the pass log over the same window (issue #145).
+	RefuseBackoff = 15 * time.Minute
 	// browserWakeCount and browserWakeAge gate a browser Lane's run: five or
 	// more due Series, or any one of them waiting this long, or Chrome stays
 	// asleep (ADR-0005 on-demand browser).