Draw no buoy for a virtual aid to navigation

A virtual aid (AIS message 21's VirtualAtoN flag) is a mark broadcast
where nothing physical stands, so drawing it as a buoy showed a mark
that is not there. The vessel source record now carries `virtual`
(false unless a source says true; any source may set it), AISStream
sets it from VirtualAtoN, and the vessel layer keeps such an aid's
disc: vesselModelSpec returns null for it and the layer gathers no
model item for it. Its card, selected card and readout add VIRTUAL
after its kind.

server/providers/vessels/ais-store.js

@@ -143,6 +143,9 @@ export function ingestAisStreamEnvelope(envelope) {
     // Use the AIS message's own report time, not server ingest wall-clock —
     // trail spacing and dead reckoning depend on true fix epochs.
     last_position_epoch: aisEpochSeconds(metadata.time_utc ?? metadata.TimeUtc),
+    // A virtual aid is broadcast where nothing physical stands. Only such a
+    // row carries the field, so ship rows stay their size.
+    ...(aidReport && message.VirtualAtoN === true && { virtual: true }),
     _updatedAt: Date.now(),
   });