feat: Implement quest reward system with item selection and storage; update related services and database schema

DorkNet.Server/Data/Entities/GameRewardSelectionEntity.cs

@@ -12,4 +12,15 @@ public class GameRewardSelectionEntity
     public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
     public DateTime? SelectedAt { get; set; }
     public int? SelectedGiftDropId { get; set; }
+
+    /// <summary>The three store-item ids offered as the choose-1-of-3
+    /// reward. Persisted so re-fetching the pending reward is stable and
+    /// <c>/select</c> can grant exactly what was shown. 0 = empty slot.</summary>
+    public long Offer1ItemId { get; set; }
+    public long Offer2ItemId { get; set; }
+    public long Offer3ItemId { get; set; }
+
+    /// <summary>Set once the chosen item has been granted to inventory, so
+    /// a replayed <c>/select</c> can't grant twice.</summary>
+    public long GrantedItemId { get; set; }
 }