fix: 优化休息时间计算逻辑，使用计数器避免时间跳变

ActivityMonitor.cs

@@ -16,6 +16,7 @@ namespace TimerApp
         private DateTime _lastWorkStartTime;
         private TimeSpan _accumulatedWorkTime;
         private DateTime _restStartTime;
+        private int _restElapsedSeconds; // 休息已过秒数（用于避免时间计算导致的跳变）
 
         // 配置 (默认值)
         public TimeSpan WorkDuration { get; set; } = TimeSpan.FromMinutes(20);
@@ -73,10 +74,12 @@ namespace TimerApp
             if (CurrentState == MonitorState.Resting)
             {
                 // 休息模式逻辑
-                TimeSpan timeInRest = DateTime.Now - _restStartTime;
-                TimeSpan remainingRest = RestDuration - timeInRest;
+                // 使用计数器而不是时间差，避免秒数跳变
+                _restElapsedSeconds++;
+                int totalRestSeconds = (int)RestDuration.TotalSeconds;
+                int remainingSeconds = totalRestSeconds - _restElapsedSeconds;
 
-                if (remainingRest <= TimeSpan.Zero)
+                if (remainingSeconds <= 0)
                 {
                     // 休息结束
                     RestEnded?.Invoke(this, EventArgs.Empty);
@@ -84,6 +87,7 @@ namespace TimerApp
                 }
                 else
                 {
+                    TimeSpan remainingRest = TimeSpan.FromSeconds(remainingSeconds);
                     RestProgressChanged?.Invoke(this, remainingRest);
                 }
             }
@@ -130,6 +134,7 @@ namespace TimerApp
                     {
                         // 触发休息
                         _restStartTime = DateTime.Now;
+                        _restElapsedSeconds = 0; // 重置休息计数器
                         ChangeState(MonitorState.Resting);
                         RestStarted?.Invoke(this, EventArgs.Empty);
                     }
@@ -145,6 +150,7 @@ namespace TimerApp
         public void ForceRest()
         {
              _restStartTime = DateTime.Now;
+             _restElapsedSeconds = 0; // 重置休息计数器
              ChangeState(MonitorState.Resting);
              RestStarted?.Invoke(this, EventArgs.Empty);
         }
@@ -158,8 +164,11 @@ namespace TimerApp
              }
              else if (CurrentState == MonitorState.Resting)
              {
-                 TimeSpan timeInRest = DateTime.Now - _restStartTime;
-                 TimeSpan remaining = RestDuration - timeInRest;
+                 // 使用计数器计算剩余时间，保持一致性
+                 int totalRestSeconds = (int)RestDuration.TotalSeconds;
+                 int remainingSeconds = totalRestSeconds - _restElapsedSeconds;
+                 if (remainingSeconds < 0) remainingSeconds = 0;
+                 TimeSpan remaining = TimeSpan.FromSeconds(remainingSeconds);
                  RestProgressChanged?.Invoke(this, remaining);
              }
         }