feat: implement cross-batch Alipay refund reconciliation

When a refund row in an uploaded Alipay bill has no matching expense
row in the same batch (because the original purchase was uploaded in a
prior batch), the refund is now reconciled against the stored record in
bills_cleaned rather than being silently discarded.

Changes:
- analyzer/cleaners/base.py: add unresolved_refunds list to BaseCleaner
- analyzer/cleaners/alipay.py: _aggregate_refunds stores full refund
  metadata (dict); _process_expenses tracks matched keys and populates
  self.unresolved_refunds for unmatched refunds
- analyzer/server.py: thread unresolved_refunds through do_clean,
  CleanResponse, and both /clean endpoints
- server/adapter/adapter.go: add UnresolvedRefund type and field to CleanResult
- server/adapter/http/cleaner.go: deserialize unresolved_refunds from
  Python response and populate CleanResult
- server/repository/repository.go: add ReconcileRefund to BillRepository interface
- server/repository/mongo/repository.go: implement ReconcileRefund —
  full refund soft-deletes the bill, partial refund reduces amount and
  appends remark with original amount and refund order number
- server/handler/upload.go: capture clean result and call ReconcileRefund
  for each unresolved refund after saving cleaned bills
- server/model/response.go: add ReconciledRefundCount to UploadData

Also: add CLAUDE.md (@AGENTS.md), update AGENTS.md, fix DailyTrendChart
missing-date gap by filling zero-expense dates in daily map.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server/adapter/adapter.go

@@ -13,8 +13,20 @@ type CleanOptions struct {
 
 // CleanResult 清洗结果
 type CleanResult struct {
-	BillType string // 检测到的账单类型: alipay/wechat/jd
-	Output   string // 脚本输出信息
+	BillType          string             // 检测到的账单类型: alipay/wechat/jd
+	Output            string             // 脚本输出信息
+	UnresolvedRefunds []UnresolvedRefund // 本次清洗未在同批次内匹配到对应支出的退款
+}
+
+// UnresolvedRefund 本次清洗未在同批次内匹配到对应支出的退款
+type UnresolvedRefund struct {
+	OrderNo         string  // 原订单号（去除退款后缀）
+	MerchantOrderNo string  // 商家订单号（备用匹配字段）
+	RefundOrderNo   string  // 退款行自身的完整订单号（用于备注追溯）
+	Amount          float64 // 退款金额
+	Time            string  // 退款时间
+	Merchant        string  // 交易对方
+	Description     string  // 商品说明
 }
 
 // ConvertResult 格式转换结果