feat: 新增账单导出 Excel 功能

- 后端新增 /api/bills/export 接口，支持当前筛选条件导出全部记录
- 使用 excelize 库生成 xlsx 格式文件
- 前端账单管理页面添加导出按钮
- 更新 Go 版本到 1.24 以支持 excelize 依赖

server/handler/export.go

@@ -0,0 +1,134 @@
+package handler
+
+import (
+	"fmt"
+	"net/http"
+	"time"
+
+	"github.com/gin-gonic/gin"
+	"github.com/xuri/excelize/v2"
+
+	"billai-server/repository"
+)
+
+type ExportBillsRequest struct {
+	StartDate     string `form:"start_date"`
+	EndDate       string `form:"end_date"`
+	Category      string `form:"category"`
+	Type          string `form:"type"`
+	IncomeExpense string `form:"income_expense"`
+}
+
+func ExportBills(c *gin.Context) {
+	var req ExportBillsRequest
+	if err := c.ShouldBindQuery(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{
+			"result":  false,
+			"message": "参数解析失败: " + err.Error(),
+		})
+		return
+	}
+
+	filter := buildFilterFromRequest(req)
+
+	repo := repository.GetRepository()
+	if repo == nil {
+		c.JSON(http.StatusInternalServerError, gin.H{
+			"result":  false,
+			"message": "数据库未连接",
+		})
+		return
+	}
+
+	bills, err := repo.GetCleanedBills(filter)
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{
+			"result":  false,
+			"message": "查询失败: " + err.Error(),
+		})
+		return
+	}
+
+	f := excelize.NewFile()
+	sheet := "账单"
+	f.SetSheetName("Sheet1", sheet)
+
+	headers := []string{"时间", "来源", "分类", "交易对方", "商品说明", "收/支", "金额", "支付方式", "状态", "备注"}
+	for i, header := range headers {
+		cell, _ := excelize.CoordinatesToCellName(i+1, 1)
+		f.SetCellValue(sheet, cell, header)
+	}
+
+	for idx, bill := range bills {
+		row := idx + 2
+
+		f.SetCellValue(sheet, fmt.Sprintf("A%d", row), bill.Time.Time().Format("2006-01-02 15:04:05"))
+		f.SetCellValue(sheet, fmt.Sprintf("B%d", row), bill.BillType)
+		f.SetCellValue(sheet, fmt.Sprintf("C%d", row), bill.Category)
+		f.SetCellValue(sheet, fmt.Sprintf("D%d", row), bill.Merchant)
+		f.SetCellValue(sheet, fmt.Sprintf("E%d", row), bill.Description)
+		f.SetCellValue(sheet, fmt.Sprintf("F%d", row), bill.IncomeExpense)
+		f.SetCellValue(sheet, fmt.Sprintf("G%d", row), bill.Amount)
+		f.SetCellValue(sheet, fmt.Sprintf("H%d", row), bill.PayMethod)
+		f.SetCellValue(sheet, fmt.Sprintf("I%d", row), bill.Status)
+		f.SetCellValue(sheet, fmt.Sprintf("J%d", row), bill.Remark)
+	}
+
+	f.SetColWidth(sheet, "A", "A", 20)
+	f.SetColWidth(sheet, "B", "B", 8)
+	f.SetColWidth(sheet, "C", "C", 12)
+	f.SetColWidth(sheet, "D", "D", 20)
+	f.SetColWidth(sheet, "E", "E", 30)
+	f.SetColWidth(sheet, "F", "F", 8)
+	f.SetColWidth(sheet, "G", "G", 12)
+	f.SetColWidth(sheet, "H", "H", 15)
+	f.SetColWidth(sheet, "I", "I", 10)
+	f.SetColWidth(sheet, "J", "J", 20)
+
+	filename := fmt.Sprintf("bills_%s.xlsx", time.Now().Format("20060102_150405"))
+	c.Header("Content-Type", "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet")
+	c.Header("Content-Disposition", fmt.Sprintf("attachment; filename=%s", filename))
+	c.Header("Access-Control-Expose-Headers", "Content-Disposition")
+
+	if err := f.Write(c.Writer); err != nil {
+		fmt.Printf("导出 Excel 失败: %v\n", err)
+	}
+}
+
+func buildFilterFromRequest(req ExportBillsRequest) map[string]interface{} {
+	filter := make(map[string]interface{})
+
+	if req.StartDate != "" || req.EndDate != "" {
+		timeFilter := make(map[string]interface{})
+		if req.StartDate != "" {
+			startTime, err := time.ParseInLocation("2006-01-02", req.StartDate, time.Local)
+			if err == nil {
+				timeFilter["$gte"] = startTime
+			}
+		}
+		if req.EndDate != "" {
+			endTime, err := time.ParseInLocation("2006-01-02", req.EndDate, time.Local)
+			if err == nil {
+				endTime = endTime.Add(24 * time.Hour)
+				timeFilter["$lt"] = endTime
+			}
+		}
+		if len(timeFilter) > 0 {
+			filter["time"] = timeFilter
+		}
+	}
+
+	if req.Category != "" {
+		filter["category"] = req.Category
+	}
+	if req.Type != "" {
+		filter["bill_type"] = req.Type
+	}
+	if req.IncomeExpense != "" {
+		filter["income_expense"] = req.IncomeExpense
+	}
+
+	filter["is_deleted"] = false
+
+	return filter
+}