feat: 移除预算同步相关功能，简化预算管理逻辑

WebApi/Controllers/Dto/BudgetDto.cs

@@ -12,7 +12,6 @@ public class BudgetDto
     public bool IsStopped { get; set; }
     public string StartDate { get; set; } = string.Empty;
     public string Period { get; set; } = string.Empty;
-    public string LastSync { get; set; } = string.Empty;
 
     public static BudgetDto FromEntity(BudgetRecord entity, decimal currentAmount = 0, DateTime? referenceDate = null)
     {
@@ -32,8 +31,7 @@ public class BudgetDto
                 : entity.SelectedCategories.Split(','),
             IsStopped = entity.IsStopped,
             StartDate = entity.StartDate.ToString("yyyy-MM-dd"),
-            Period = entity.Type == BudgetPeriodType.Longterm ? "长期" : $"{start:yyyy-MM-dd} ~ {end:yyyy-MM-dd}",
-            LastSync = entity.LastSync?.ToString("yyyy-MM-dd HH:mm") ?? "未同步"
+            Period = entity.Type == BudgetPeriodType.Longterm ? "长期" : $"{start:yyyy-MM-dd} ~ {end:yyyy-MM-dd}"
         };
     }
 }