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/Services/ArenaTwoPickServiceWeightedRewardsTests.cs

@@ -110,11 +110,11 @@ public class ArenaTwoPickServiceWeightedRewardsTests
         // Seed catalog: two rows, same group, same WinCount=3.
         db.ArenaTwoPickRewards.Add(new ArenaTwoPickReward
         {
-            WinCount = 3, RewardGroup = 1, Weight = 1, RewardType = 9, RewardId = 0, RewardNum = 100
+            WinCount = 3, RewardGroup = 1, Weight = 1, RewardType = (UserGoodsType)9, RewardId = 0, RewardNum = 100
         });
         db.ArenaTwoPickRewards.Add(new ArenaTwoPickReward
         {
-            WinCount = 3, RewardGroup = 1, Weight = 9, RewardType = 9, RewardId = 0, RewardNum = 999
+            WinCount = 3, RewardGroup = 1, Weight = 9, RewardType = (UserGoodsType)9, RewardId = 0, RewardNum = 999
         });
         await db.SaveChangesAsync();
 
@@ -134,11 +134,11 @@ public class ArenaTwoPickServiceWeightedRewardsTests
 
         db.ArenaTwoPickRewards.Add(new ArenaTwoPickReward
         {
-            WinCount = 2, RewardGroup = 1, Weight = 0, RewardType = 9, RewardId = 0, RewardNum = 9999
+            WinCount = 2, RewardGroup = 1, Weight = 0, RewardType = (UserGoodsType)9, RewardId = 0, RewardNum = 9999
         });
         db.ArenaTwoPickRewards.Add(new ArenaTwoPickReward
         {
-            WinCount = 2, RewardGroup = 1, Weight = 1, RewardType = 9, RewardId = 0, RewardNum = 500
+            WinCount = 2, RewardGroup = 1, Weight = 1, RewardType = (UserGoodsType)9, RewardId = 0, RewardNum = 500
         });
         await db.SaveChangesAsync();
 
@@ -158,7 +158,7 @@ public class ArenaTwoPickServiceWeightedRewardsTests
 
         db.ArenaTwoPickRewards.Add(new ArenaTwoPickReward
         {
-            WinCount = 1, RewardGroup = 1, Weight = 1, RewardType = 9, RewardId = 0, RewardNum = 0
+            WinCount = 1, RewardGroup = 1, Weight = 1, RewardType = (UserGoodsType)9, RewardId = 0, RewardNum = 0
         });
         await db.SaveChangesAsync();
 
@@ -189,7 +189,7 @@ public class ArenaTwoPickServiceWeightedRewardsTests
         // still satisfies the >=5 check so Retire works regardless).
         db.ArenaTwoPickRewards.Add(new ArenaTwoPickReward
         {
-            WinCount = 0, RewardGroup = 1, Weight = 1, RewardType = 9, RewardId = 0, RewardNum = 50
+            WinCount = 0, RewardGroup = 1, Weight = 1, RewardType = (UserGoodsType)9, RewardId = 0, RewardNum = 50
         });
         await db.SaveChangesAsync();