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.Bootstrap/Importers/ArenaTwoPickRewardImporter.cs

@@ -1,6 +1,7 @@
 using Microsoft.EntityFrameworkCore;
 using SVSim.Bootstrap.Models.Seed;
 using SVSim.Database;
+using SVSim.Database.Enums;
 using SVSim.Database.Models;
 
 namespace SVSim.Bootstrap.Importers;
@@ -27,7 +28,7 @@ public class ArenaTwoPickRewardImporter
         int upserted = 0;
         foreach (var s in seeds)
         {
-            if (existing.TryGetValue((s.WinCount, s.RewardGroup, s.RewardType, s.RewardId, s.RewardNum), out var row))
+            if (existing.TryGetValue((s.WinCount, s.RewardGroup, (UserGoodsType)s.RewardType, s.RewardId, s.RewardNum), out var row))
             {
                 row.Weight = s.Weight;
             }
@@ -38,7 +39,7 @@ public class ArenaTwoPickRewardImporter
                     WinCount    = s.WinCount,
                     RewardGroup = s.RewardGroup,
                     Weight      = s.Weight,
-                    RewardType  = s.RewardType,
+                    RewardType  = (UserGoodsType)s.RewardType,
                     RewardId    = s.RewardId,
                     RewardNum   = s.RewardNum,
                 });