Implement Enhancements, Mainline modifiers and Maneuvers; fix unplayable track

src/engine/track.ts

@@ -79,8 +79,9 @@ type PortPair = readonly [Port, Port];
  */
 function connectionsFor(card: TrackCard): readonly PortPair[] {
   switch (card.geometry.kind) {
-    // A Modifier is not track: nothing connects to it and no train may enter (§9).
+    // Neither a Modifier nor a Space-use card is track: nothing connects, no train may enter.
     case 'modifier':
+    case 'spaceUse':
       return [];
     case 'limits':
       return [['e', 'w']];