fix: handle null pool and adjust week calculation rules

src/CMSMicroservice.Application/CommissionCQ/Queries/GetAvailableWeeks/GetAvailableWeeksQueryHandler.cs

@@ -113,8 +113,8 @@ public class GetAvailableWeeksQueryHandler : IRequestHandler<GetAvailableWeeksQu
         var calendar = CultureInfo.InvariantCulture.Calendar;
         var weekOfYear = calendar.GetWeekOfYear(
             date, 
-            CalendarWeekRule.FirstFourDayWeek, 
-            DayOfWeek.Monday);
+            CalendarWeekRule.FirstDay, 
+            DayOfWeek.Saturday);
         
         return $"{date.Year}-W{weekOfYear:D2}";
     }

src/CMSMicroservice.Application/CommissionCQ/Queries/GetWeeklyCommissionPool/GetWeeklyCommissionPoolQueryHandler.cs

@@ -27,6 +27,6 @@ public class GetWeeklyCommissionPoolQueryHandler : IRequestHandler<GetWeeklyComm
             })
             .FirstOrDefaultAsync(cancellationToken);
 
-        return pool;
+        return pool??new WeeklyCommissionPoolDto();
     }
 }