add shel

src/HSchool.Content/MapLayout.cs

@@ -55,6 +55,12 @@ public sealed class RoomNode
     /// <summary>Optional designation such as a classroom number. The def label still supplies the noun.</summary>
     public string? Label { get; init; }
 
+    /// <summary>
+    /// Homeroom seat count. Capacity is <c>SeatThing.PupilSlots × Seats</c>. Named
+    /// <see cref="Slots"/> stay on rooms whose furnishing actually varies.
+    /// </summary>
+    public int Seats { get; init; }
+
     public IReadOnlyList<SlotFill> Slots { get; init; } = [];
 }