Prebuilt deck purchasing and fixes

SVSim.Database/Models/BuildDeckProductEntry.cs

@@ -0,0 +1,32 @@
+using SVSim.Database.Common;
+
+namespace SVSim.Database.Models;
+
+/// <summary>
+/// One purchasable prebuilt-deck product. PK = wire product_id. FK SeriesId.
+/// Pricing columns are nullable; either Crystal or Rupy pair (or both, both zero for free) must
+/// be populated for an enabled product. The Intro/Regular pair captures the two-tier pricing
+/// pattern: Intro applies to the first purchase, Regular to subsequent. For PurchaseNumMax=1
+/// products, Regular stays null and only Intro is ever served.
+/// </summary>
+public class BuildDeckProductEntry : BaseEntity<int>
+{
+    public int SeriesId { get; set; }
+    public int LeaderId { get; set; }
+    public string DeckCode { get; set; } = string.Empty;
+    public string ProductNameKey { get; set; } = string.Empty;   // BDPN_*
+    public long FeaturedCardId { get; set; }
+    public int PurchaseNumMax { get; set; }
+
+    public int? IntroPriceCrystal { get; set; }
+    public int? RegularPriceCrystal { get; set; }
+    public int? IntroPriceRupy { get; set; }
+    public int? RegularPriceRupy { get; set; }
+
+    public bool IsEnabled { get; set; }
+
+    public List<BuildDeckProductCardEntry> Cards { get; set; } = new();
+    public List<BuildDeckProductRewardEntry> Rewards { get; set; } = new();
+
+    public BuildDeckSeriesEntry? Series { get; set; }
+}