feat(db): add ViewerPresent entity for unified gift inbox

SVSim.Database/Models/ViewerPresent.cs

@@ -0,0 +1,57 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace SVSim.Database.Models;
+
+/// <summary>
+/// One row per gift in a viewer's inbox. Replaces the tutorial-only
+/// <c>ViewerClaimedTutorialGift</c> receipts model with a unified status-enum row that
+/// serves both /gift/top + /gift/receive_gift (prod) and /tutorial/gift_top +
+/// /tutorial/gift_receive (tutorial alias).
+/// </summary>
+public class ViewerPresent
+{
+    public long Id { get; set; }
+
+    public long ViewerId { get; set; }
+    public Viewer Viewer { get; set; } = null!;
+
+    /// <summary>Wire id ("71409625" in the prod capture). String to match the wire.</summary>
+    public string PresentId { get; set; } = string.Empty;
+
+    public PresentStatus Status { get; set; }
+
+    /// <summary>UserGoodsType-compatible int. Wire is stringified — see PresentMapper.</summary>
+    public int RewardType { get; set; }
+    public long RewardDetailId { get; set; }
+    public long RewardCount { get; set; }
+    public int ConditionNumber { get; set; }
+    public int PresentLimitType { get; set; }
+    public long RewardLimitTime { get; set; }
+    public int? ItemType { get; set; }
+    public string Message { get; set; } = string.Empty;
+
+    public DateTime CreatedAt { get; set; }
+    public DateTime? ClaimedAt { get; set; }
+
+    /// <summary>
+    /// Free-form provenance tag for future producers ("tutorial", "challenge_win",
+    /// "payment_refund:&lt;txid&gt;", "event:&lt;id&gt;"). Nothing in the receive handler reads
+    /// this today — the tutorial-step advance is route-gated, not Source-gated.
+    /// </summary>
+    public string? Source { get; set; }
+
+    /// <summary>
+    /// EF Core optimistic concurrency for the claim path. Two concurrent claims of the
+    /// same PresentId: first wins, second's CommitAsync throws DbUpdateConcurrencyException.
+    /// </summary>
+    [Timestamp]
+    public byte[] RowVersion { get; set; } = Array.Empty<byte>();
+}
+
+public enum PresentStatus : byte
+{
+    Unclaimed = 0,
+    Claimed = 1,
+    Deleted = 2,
+    Expired = 3,
+}