refactor: type reward_type columns as UserGoodsType enum

Replace bare `int RewardType` on 12 catalog/reward entities and GrantedReward
with the existing UserGoodsType enum. Verified against the decompiled client:
every wire reward_type decodes through the single Wizard.UserGoods.Type enum, so
one enum is correct across all endpoint families (item_type is a separate
Item.Type axis, left untouched). EF stores the enum as the same int column, so
there is no migration.

- Importers cast seed int -> UserGoodsType at the ingest boundary.
- New GrantedReward.ToRewardList() extension replaces 8 copy-pasted
  GrantedReward -> RewardListEntry projections.
- Fix 3 .ToString() sites that would otherwise emit enum names ("Crystal")
  instead of the int wire value ("2").
- Wire DTOs keep int; the enum is widened to int at the wire boundary only.

Build green; 962/962 tests pass.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

SVSim.UnitTests/Importers/ArenaTwoPickRewardImporterTests.cs

@@ -2,6 +2,7 @@ using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.DependencyInjection;
 using SVSim.Bootstrap.Importers;
 using SVSim.Database;
+using SVSim.Database.Enums;
 using SVSim.UnitTests.Infrastructure;
 
 namespace SVSim.UnitTests.Importers;
@@ -32,12 +33,12 @@ public class ArenaTwoPickRewardImporterTests
 
         var w0 = rows.Where(r => r.WinCount == 0).ToList();
         Assert.That(w0.Count, Is.EqualTo(2));
-        Assert.That(w0.Single(r => r.RewardType == 4).RewardNum, Is.EqualTo(1));
-        Assert.That(w0.Single(r => r.RewardType == 9).RewardNum, Is.EqualTo(100));
+        Assert.That(w0.Single(r => r.RewardType == (UserGoodsType)4).RewardNum, Is.EqualTo(1));
+        Assert.That(w0.Single(r => r.RewardType == (UserGoodsType)9).RewardNum, Is.EqualTo(100));
 
         var w5 = rows.Where(r => r.WinCount == 5).ToList();
-        Assert.That(w5.Single(r => r.RewardType == 4).RewardNum, Is.EqualTo(1));
-        Assert.That(w5.Single(r => r.RewardType == 9).RewardNum, Is.EqualTo(1000));
+        Assert.That(w5.Single(r => r.RewardType == (UserGoodsType)4).RewardNum, Is.EqualTo(1));
+        Assert.That(w5.Single(r => r.RewardType == (UserGoodsType)9).RewardNum, Is.EqualTo(1000));
 
         // New columns: all rows should have weight=1 and win5 should span 2 distinct groups.
         Assert.That(w5.All(r => r.Weight == 1), "all win5 rows should have Weight=1");