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/model/response.go

@@ -2,13 +2,14 @@ package model
 
 // UploadData 上传响应数据
 type UploadData struct {
-	BillType         string `json:"bill_type,omitempty"`          // alipay/wechat/jd
-	FileURL          string `json:"file_url,omitempty"`           // 下载链接
-	FileName         string `json:"file_name,omitempty"`          // 文件名
-	RawCount         int    `json:"raw_count,omitempty"`          // 存储到原始数据集合的记录数
-	CleanedCount     int    `json:"cleaned_count,omitempty"`      // 存储到清洗后数据集合的记录数
-	DuplicateCount   int    `json:"duplicate_count,omitempty"`    // 重复跳过的记录数
-	JDRelatedDeleted int64  `json:"jd_related_deleted,omitempty"` // 软删除的京东关联记录数（其他来源中描述包含京东订单号的记录）
+	BillType              string `json:"bill_type,omitempty"`               // alipay/wechat/jd
+	FileURL               string `json:"file_url,omitempty"`                // 下载链接
+	FileName              string `json:"file_name,omitempty"`               // 文件名
+	RawCount              int    `json:"raw_count,omitempty"`               // 存储到原始数据集合的记录数
+	CleanedCount          int    `json:"cleaned_count,omitempty"`           // 存储到清洗后数据集合的记录数
+	DuplicateCount        int    `json:"duplicate_count,omitempty"`         // 重复跳过的记录数
+	JDRelatedDeleted      int64  `json:"jd_related_deleted,omitempty"`      // 软删除的京东关联记录数（其他来源中描述包含京东订单号的记录）
+	ReconciledRefundCount int    `json:"reconciled_refund_count,omitempty"` // 跨批次核销的退款记录数
 }
 
 // UploadResponse 上传响应