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/Controllers/LeaderSkinShopControllerTests.cs

@@ -4,6 +4,7 @@ using System.Text.Json;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.DependencyInjection;
 using SVSim.Database;
+using SVSim.Database.Enums;
 using SVSim.Database.Models;
 using SVSim.UnitTests.Infrastructure;
 
@@ -46,19 +47,19 @@ public class LeaderSkinShopControllerTests
                     Id = 90011, SeriesId = 9001, LeaderSkinId = 9101,
                     ProductNameKey = "LSPPN_test_1", IntroductionKey = "LSPI_test_1", CvNameKey = "LSPCN_test_1",
                     SinglePriceCrystal = 500, SinglePriceRupy = 500, IsEnabled = true,
-                    Rewards = { new LeaderSkinShopProductRewardEntry { OrderIndex = 0, RewardType = 10, RewardDetailId = 9101, RewardNumber = 1 } },
+                    Rewards = { new LeaderSkinShopProductRewardEntry { OrderIndex = 0, RewardType = (UserGoodsType)10, RewardDetailId = 9101, RewardNumber = 1 } },
                 },
                 new LeaderSkinShopProductEntry
                 {
                     Id = 90012, SeriesId = 9001, LeaderSkinId = 9102,
                     ProductNameKey = "LSPPN_test_2", IntroductionKey = "LSPI_test_2", CvNameKey = "LSPCN_test_2",
                     SinglePriceCrystal = 500, SinglePriceRupy = 500, IsEnabled = true,
-                    Rewards = { new LeaderSkinShopProductRewardEntry { OrderIndex = 0, RewardType = 10, RewardDetailId = 9102, RewardNumber = 1 } },
+                    Rewards = { new LeaderSkinShopProductRewardEntry { OrderIndex = 0, RewardType = (UserGoodsType)10, RewardDetailId = 9102, RewardNumber = 1 } },
                 },
             },
             SetCompletionRewards =
             {
-                new LeaderSkinShopSeriesRewardEntry { OrderIndex = 0, RewardType = 9, RewardDetailId = 0, RewardNumber = 500 },
+                new LeaderSkinShopSeriesRewardEntry { OrderIndex = 0, RewardType = (UserGoodsType)9, RewardDetailId = 0, RewardNumber = 500 },
             },
         });
         await db.SaveChangesAsync();