fix(gift): drop RowVersion (SQLite incompatible) + restore wire reward_type map

[Timestamp] byte[] doesn't work under SQLite (the test backend) — EF
expects the DB to populate it on insert, but SQLite has no equivalent
of Postgres's xmin. The WHERE Status = Unclaimed filter plus
IInventoryService's viewer-level concurrency is the practical defense;
RowVersion was only a backstop. Regenerated the migration without the
RowVersion column.

Wire reward_type on the gift endpoint uses a gift-specific scheme that
diverges from UserGoodsType for currencies: wire 1 = Crystal (enum=2),
wire 9 = Rupy (enum=9), wire 4 = Item (enum=4). A naked cast resolves
wire 1 to UserGoodsType.RedEther and silently grants the wrong wallet
— restored the explicit WireRewardTypeToUserGoodsType map from the old
tutorial controller.

Retrofits existing GiftControllerTests to call SeedTutorialPresentsAsync
on the new helper (RegisterViewer doesn't auto-seed; only the prod
signup path does). All 7 existing tests pass.

SVSim.Database/Models/ViewerPresent.cs

@@ -1,5 +1,3 @@
-using System.ComponentModel.DataAnnotations;
-
 namespace SVSim.Database.Models;
 
 /// <summary>
@@ -39,13 +37,6 @@ public class ViewerPresent
     /// 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