Name the real gate altitude and repaint coverage rows at once

The Transit prompt said "Fly below 3,000 km", but the closed gate opens at
2,850 km; it now names the enter threshold, as Bike Share does. When the
camera changes coverage, Transit and Bike Share ask the Layers panel to
repaint instead of leaving the old prompt up until the next 15 s / 60 s tick.

docs/CURRENT-STATE.md

@@ -1819,7 +1819,7 @@ errors.
 
 Transit and Bike Share report the same kind of guidance when no feed or system
 covers the view, instead of an undated `never`. Above their altitude gates the
-rows read `GTFS-RT · Fly below 3,000 km to a covered region` and
+rows read `GTFS-RT · Fly below 2,850 km to a covered region` and
 `GBFS · Fly below 48 km to a covered city`; lower down over a city neither
 covers (London, Tokyo) they read `GTFS-RT · No feed here yet · N regions
 available` and `GBFS · No bike share here yet · N systems available`, N being