feat: implement WeChat cross-batch refund reconciliation and fix misc issues

WeChat cross-batch refund reconciliation:
- Add OriginalAmount field to CleanedBill for accurate cumulative refund math
- DeduplicateRawFile detects WeChat status-update rows (已退款/已全额退款) and
  emits WechatRefundUpdates for Go-side reconciliation (Scenario 1)
- WechatPy cleaner surfaces -退款 income rows with no same-batch expense match
  as unresolved_refunds for Go ReconcileRefund (Scenario 2)
- Add ReconcileWechatRefund to repository interface and MongoDB implementation
- upload.go step 15 iterates WechatRefundUpdates and reconciles against bills_cleaned

Bug fixes:
- ReviewStats: add nil repo check to prevent panic when DB is not connected
- JWT: remove hardcoded fallback secret; return 500/401 if JWTSecret not configured
- Remove unused parsePageParam dead code and its strconv import
- BillDetailDrawer: show 不计收支 amount in muted gray instead of red
- test_jd_cleaner.py: replace hardcoded D:\Projects\BillAI path with dynamic __file__ resolution

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

server/repository/mongo/repository.go

@@ -567,8 +567,83 @@ func (r *Repository) ReconcileRefund(billType, orderNo, merchantOrderNo string,
 	return true, nil
 }
 
-// 建议: 为提升 ReconcileRefund 查询性能，可为 bills_cleaned 添加索引
-// {transaction_id:1, bill_type:1} 和 {merchant_order_no:1, bill_type:1}（与现有"无索引"问题一并处理）
+// ReconcileWechatRefund 将跨批次微信退款核销到已存储的清洗后账单
+// 微信"当前状态"字段为累计退款金额，使用 original_amount（入库时原始金额）计算剩余
+func (r *Repository) ReconcileWechatRefund(transactionID string, fullRefund bool, cumulativeRefundAmount float64) (bool, error) {
+	if r.cleanedCollection == nil {
+		return false, fmt.Errorf("cleaned collection not initialized")
+	}
+	if transactionID == "" {
+		return false, nil
+	}
+
+	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+	defer cancel()
+
+	filter := bson.M{
+		"bill_type":      "wechat",
+		"transaction_id": transactionID,
+		"is_deleted":     bson.M{"$ne": true},
+	}
+
+	var bill model.CleanedBill
+	if err := r.cleanedCollection.FindOne(ctx, filter).Decode(&bill); err != nil {
+		if err == mongo.ErrNoDocuments {
+			return false, nil
+		}
+		return false, fmt.Errorf("查询待核销微信账单失败: %w", err)
+	}
+
+	now := time.Now()
+
+	if fullRefund {
+		update := bson.M{"$set": bson.M{
+			"is_deleted": true,
+			"updated_at": now,
+			"remark":     fmt.Sprintf("[退款核销]全额退款;%s", bill.Remark),
+		}}
+		_, err := r.cleanedCollection.UpdateOne(ctx, bson.M{"_id": bill.ID}, update)
+		if err != nil {
+			return false, fmt.Errorf("核销微信全额退款失败: %w", err)
+		}
+		return true, nil
+	}
+
+	// 部分退款：用原始金额（original_amount）减去累计退款金额得到剩余
+	originalAmount := bill.OriginalAmount
+	if originalAmount <= 0 {
+		originalAmount = bill.Amount // 兼容旧记录（无 original_amount 字段）
+	}
+	remaining := originalAmount - cumulativeRefundAmount
+
+	if remaining <= refundEpsilon {
+		update := bson.M{"$set": bson.M{
+			"is_deleted": true,
+			"updated_at": now,
+			"remark":     fmt.Sprintf("[退款核销]全额退款%.2f元(原金额%.2f元);%s", cumulativeRefundAmount, originalAmount, bill.Remark),
+		}}
+		_, err := r.cleanedCollection.UpdateOne(ctx, bson.M{"_id": bill.ID}, update)
+		if err != nil {
+			return false, fmt.Errorf("核销微信退款失败: %w", err)
+		}
+		return true, nil
+	}
+
+	remaining = math.Round(remaining*100) / 100
+	update := bson.M{"$set": bson.M{
+		"amount":     remaining,
+		"updated_at": now,
+		"remark":     fmt.Sprintf("原金额%.2f元,已退款%.2f元;%s", originalAmount, cumulativeRefundAmount, bill.Remark),
+	}}
+	_, err := r.cleanedCollection.UpdateOne(ctx, bson.M{"_id": bill.ID}, update)
+	if err != nil {
+		return false, fmt.Errorf("核销微信退款失败: %w", err)
+	}
+	return true, nil
+}
+
+// 建议: 为提升查询性能，可为 bills_cleaned 添加索引
+// {transaction_id:1, bill_type:1} 和 {merchant_order_no:1, bill_type:1}
 
 // GetClient 获取 MongoDB 客户端（用于兼容旧代码）
 func (r *Repository) GetClient() *mongo.Client {