fix: use current culture to adjust first days of the week

Author: czarkoff

src/Models/Statistics.cs

@@ -1,6 +1,6 @@
 using System;
 using System.Collections.Generic;
-
+using System.Globalization;
 using LiveChartsCore;
 using LiveChartsCore.Defaults;
 using LiveChartsCore.SkiaSharpView;
@@ -138,7 +138,7 @@ public class Statistics
         public Statistics()
         {
             _today = DateTime.Now.ToLocalTime().Date;
-            _thisWeekStart = _today.AddSeconds(-(int)_today.DayOfWeek * 3600 * 24);
+            _thisWeekStart = _today.AddDays(-7 + (int)_today.DayOfWeek + (int)CultureInfo.CurrentCulture.DateTimeFormat.FirstDayOfWeek);
             _thisMonthStart = _today.AddDays(1 - _today.Day);
 
             All = new StatisticsReport(StaticsticsMode.All, DateTime.MinValue);