Prebuilt deck purchasing and fixes

SVSim.Database/Models/BuildDeckProductRewardEntry.cs

@@ -0,0 +1,18 @@
+using Microsoft.EntityFrameworkCore;
+
+namespace SVSim.Database.Models;
+
+/// <summary>
+/// One per-buy reward attached to a prebuilt-deck product. Owned by BuildDeckProductEntry.
+/// Wire shape: one entry of the product-level `rewards` dict in /build_deck/info, keyed by
+/// RewardIndex (the wire string keys "1","2","3").
+/// </summary>
+[Owned]
+public class BuildDeckProductRewardEntry
+{
+    public int RewardIndex { get; set; }
+    public int RewardType { get; set; }   // Wizard.UserGoods.Type
+    public long RewardDetailId { get; set; }
+    public int RewardNumber { get; set; }
+    public int MessageId { get; set; }
+}