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>

web/src/lib/components/analysis/DailyTrendChart.svelte

@@ -199,6 +199,20 @@
       dayData.set(category, (dayData.get(category) || 0) + amount);
     });
 
+    // 填充缺失的日期（零支出日期）
+    const now = new Date();
+    const allDates: string[] = [];
+    const cursor = new Date(cutoffDate);
+    while (cursor <= now) {
+      allDates.push(formatLocalDate(cursor));
+      cursor.setDate(cursor.getDate() + 1);
+    }
+    allDates.forEach(dateStr => {
+      if (!dailyMap.has(dateStr)) {
+        dailyMap.set(dateStr, new Map());
+      }
+    });
+
     const dayCount = dailyMap.size;
     
     // 根据天数决定聚合粒度