feat(db): add gacha-point balance + received tables

SVSim.Database/SVSimDbContext.cs

@@ -167,6 +167,16 @@ public class SVSimDbContext : DbContext
             b.HasIndex("ViewerId", "ProductId").IsUnique();
         });
 
+        modelBuilder.Entity<Viewer>().OwnsMany(v => v.GachaPointBalances, b =>
+        {
+            b.HasIndex("ViewerId", "PackId").IsUnique();
+        });
+
+        modelBuilder.Entity<Viewer>().OwnsMany(v => v.GachaPointReceived, b =>
+        {
+            b.HasIndex("ViewerId", "PackId", "CardId").IsUnique();
+        });
+
         // A given social account links to exactly one viewer — two viewers cannot share the same
         // Steam (or Facebook, etc.) account. This is the dedup backstop the auth handler's find-
         // or-link path (SteamSessionAuthenticationHandler) relies on: two concurrent first-Steam-