refactor(pet): 重构宠物模块实体与接口

1. 将原Pet实体重命名为UserPet，新增PetTemplate模板实体拆分宠物模板与实例数据
2. 调整IPetService泛型参数为IBaseService<UserPet>
3. 补充宠物模板相关字段与查询逻辑，完善创建默认宠物的流程
4. 替换所有Pet实体引用为UserPet，修正相关服务层查询与更新逻辑

QYZH.InteractiveMagazine.Service/WxMallService.cs

@@ -495,7 +495,7 @@ public class WxMallService(
         logger.LogInformation("宠物换肤，UserId: {UserId}, SkinId: {SkinId}", userId, input.SkinId);
 
         // 查询用户宠物
-        var pet = await exchangeRecordRepository.Context.Queryable<Pet>()
+        var pet = await exchangeRecordRepository.Context.Queryable<UserPet>()
             .Where(p => p.UserId == userId && !p.IsDeleted)
             .FirstAsync();
 
@@ -505,7 +505,7 @@ public class WxMallService(
         if (input.SkinId == 0)
         {
             // 恢复默认皮肤
-            await exchangeRecordRepository.Context.Updateable<Pet>()
+            await exchangeRecordRepository.Context.Updateable<UserPet>()
                 .SetColumns(p => p.CurrentSkinId == 0)
                 .SetColumns(p => p.UpdatedAt == DateTime.Now)
                 .Where(p => p.Id == pet.Id)
@@ -535,7 +535,7 @@ public class WxMallService(
             throw new BusinessException("您尚未拥有该皮肤，请先兑换", 400);
 
         // 换肤
-        await exchangeRecordRepository.Context.Updateable<Pet>()
+        await exchangeRecordRepository.Context.Updateable<UserPet>()
             .SetColumns(p => p.CurrentSkinId == skin.Id)
             .SetColumns(p => p.UpdatedAt == DateTime.Now)
             .Where(p => p.Id == pet.Id)