重构预算管理模块，添加预算记录和服务，更新相关API，优化预算统计逻辑

Entity/BudgetRecord.cs

@@ -0,0 +1,83 @@
+namespace Entity;
+
+/// <summary>
+/// 预算管理
+/// </summary>
+public class BudgetRecord : BaseEntity
+{
+    /// <summary>
+    /// 预算名称
+    /// </summary>
+    public string Name { get; set; } = string.Empty;
+
+    /// <summary>
+    /// 统计周期
+    /// </summary>
+    public BudgetPeriodType Type { get; set; } = BudgetPeriodType.Month;
+
+    /// <summary>
+    /// 预算金额
+    /// </summary>
+    public decimal Limit { get; set; }
+
+    /// <summary>
+    /// 预算类别
+    /// </summary>
+    public BudgetCategory Category { get; set; }
+
+    /// <summary>
+    /// 相关分类 (逗号分隔的分类名称)
+    /// </summary>
+    public string SelectedCategories { get; set; } = string.Empty;
+
+    /// <summary>
+    /// 是否停止
+    /// </summary>
+    public bool IsStopped { get; set; } = false;
+
+    /// <summary>
+    /// 开始日期
+    /// </summary>
+    public DateTime StartDate { get; set; } = DateTime.Now;
+
+    /// <summary>
+    /// 上次同步时间
+    /// </summary>
+    public DateTime? LastSync { get; set; }
+}
+
+public enum BudgetPeriodType
+{
+    /// <summary>
+    /// 周
+    /// </summary>
+    Week,
+    /// <summary>
+    /// 月
+    /// </summary>
+    Month,
+    /// <summary>
+    /// 年
+    /// </summary>
+    Year,
+    /// <summary>
+    /// 长期
+    /// </summary>
+    Longterm
+}
+
+public enum BudgetCategory
+{
+    /// <summary>
+    /// 支出
+    /// </summary>
+    Expense = 0,
+    /// <summary>
+    /// 收入
+    /// </summary>
+    Income = 1,
+    /// <summary>
+    /// 存款
+    /// </summary>
+    Savings = 2
+}