fix(flights): start a new grounded aircraft on the floor under its delayed position

The fleet draws a grounded contact at its delayed position lifted onto the floor under it, but a new billboard was created at the delayed position without that lift. A taxiing aircraft whose reported fix sat lower than the ground under its delayed position started on the fix's floor and then rose on the next fleet tick. Creation now applies the same floor the fleet pass does.

src/layers/flights/snapshotRenderer.js

@@ -181,10 +181,20 @@ export function createFlightSnapshotRenderer({
       } else {
         // Start where the fleet pass will draw it: the fleet renders behind
         // real time, so a fresh contact's displayed position is its fix
-        // projected back to that delayed time. Creating it at the raw fix drew
-        // it ahead until the next fleet tick snapped it back.
+        // projected back to that delayed time, and a grounded contact is then
+        // lifted onto the floor under that delayed position. Creating it at
+        // the raw fix drew it ahead until the next fleet tick snapped it back;
+        // skipping the floor started a taxiing contact low and then raised it.
+        const delayed = motion._deadReckon(icao24, new Cesium.Cartesian3());
         const displayed =
-          motion._deadReckon(icao24, new Cesium.Cartesian3()) || position;
+          (delayed &&
+            motion._floorGroundedDisplayPosition(
+              icao24,
+              flightState.records.data.get(icao24) || meta,
+              delayed,
+              rendering._modelOwnsVisual(icao24),
+            )) ||
+          position;
         const bb = flightState._billboardCollection.add({
           position: displayed,
           image: aircraftIcon(rendering._iconKind(icao24, meta.klass)),