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

Repository/BudgetRepository.cs

@@ -0,0 +1,36 @@
+namespace Repository;
+
+public interface IBudgetRepository : IBaseRepository<BudgetRecord>
+{
+    Task<decimal> GetCurrentAmountAsync(BudgetRecord budget, DateTime startDate, DateTime endDate);
+}
+
+public class BudgetRepository(IFreeSql freeSql) : BaseRepository<BudgetRecord>(freeSql), IBudgetRepository
+{
+    public async Task<decimal> GetCurrentAmountAsync(BudgetRecord budget, DateTime startDate, DateTime endDate)
+    {
+        var query = FreeSql.Select<TransactionRecord>()
+            .Where(t => t.OccurredAt >= startDate && t.OccurredAt <= endDate);
+
+        if (!string.IsNullOrEmpty(budget.SelectedCategories))
+        {
+            var categoryList = budget.SelectedCategories.Split(',');
+            query = query.Where(t => categoryList.Contains(t.Classify));
+        }
+
+        if (budget.Category == BudgetCategory.Expense)
+        {
+            query = query.Where(t => t.Type == TransactionType.Expense);
+        }
+        else if (budget.Category == BudgetCategory.Income)
+        {
+            query = query.Where(t => t.Type == TransactionType.Income);
+        }
+        else if (budget.Category == BudgetCategory.Savings)
+        {
+            query = query.Where(t => t.Type == TransactionType.None);
+        }
+
+        return await query.SumAsync(t => t.Amount);
+    }
+}