Prebuilt deck purchasing and fixes

SVSim.Database/Models/BuildDeckProductCardEntry.cs

@@ -0,0 +1,17 @@
+using Microsoft.EntityFrameworkCore;
+
+namespace SVSim.Database.Models;
+
+/// <summary>
+/// One card in a prebuilt-deck product's 40-card list. Owned by BuildDeckProductEntry.
+/// Shape mirrors `build_deck_package_master.csv` rows: (ProductId, CardId, Number, IsSpot).
+/// IsSpot=true marks the special prize/featured cards rendered in the separate _spotCardRoot
+/// panel by BuildDeckProductDetail.cs.
+/// </summary>
+[Owned]
+public class BuildDeckProductCardEntry
+{
+    public long CardId { get; set; }
+    public int Number { get; set; }
+    public bool IsSpot { get; set; }
+}