feat: 新增一键确认收款接口

问题: 原recordPayment只创建Pending支付记录,不更新账单状态
用户点击确认收款后需要再次审核才能生效

解决方案:
- 新增POST /api/admin/v1/billings/{id}/payments/confirm接口
- 内部原子化执行: 创建支付+自动审核+更新账单状态
- 保留原recordPayment接口用于需要审核的场景

新增文件:
- ConfirmPaymentCommand.cs
- ConfirmPaymentCommandHandler.cs
- ConfirmPaymentCommandValidator.cs

src/Application/TakeoutSaaS.Application/App/Billings/Handlers/ConfirmPaymentCommandHandler.cs

@@ -0,0 +1,99 @@
+using MediatR;
+using TakeoutSaaS.Application.App.Billings.Commands;
+using TakeoutSaaS.Application.App.Billings.Dto;
+using TakeoutSaaS.Domain.Tenants.Entities;
+using TakeoutSaaS.Domain.Tenants.Enums;
+using TakeoutSaaS.Domain.Tenants.Repositories;
+using TakeoutSaaS.Shared.Abstractions.Constants;
+using TakeoutSaaS.Shared.Abstractions.Exceptions;
+using TakeoutSaaS.Shared.Abstractions.Ids;
+using TakeoutSaaS.Shared.Abstractions.Security;
+
+namespace TakeoutSaaS.Application.App.Billings.Handlers;
+
+/// <summary>
+/// 一键确认收款处理器（记录支付 + 立即审核通过 + 同步更新账单已收金额/状态）。
+/// </summary>
+public sealed class ConfirmPaymentCommandHandler(
+    ITenantBillingRepository billingRepository,
+    ITenantPaymentRepository paymentRepository,
+    IIdGenerator idGenerator,
+    ICurrentUserAccessor currentUserAccessor)
+    : IRequestHandler<ConfirmPaymentCommand, PaymentRecordDto>
+{
+    /// <inheritdoc />
+    public async Task<PaymentRecordDto> Handle(ConfirmPaymentCommand request, CancellationToken cancellationToken)
+    {
+        // 1. 校验操作者身份（用于写入 VerifiedBy）
+        if (!currentUserAccessor.IsAuthenticated || currentUserAccessor.UserId <= 0)
+        {
+            throw new BusinessException(ErrorCodes.Unauthorized, "未登录或无效的操作者身份");
+        }
+
+        // 2. (空行后) 查询账单
+        var billing = await billingRepository.FindByIdAsync(request.BillingId, cancellationToken);
+        if (billing is null)
+        {
+            throw new BusinessException(ErrorCodes.NotFound, "账单不存在");
+        }
+
+        // 3. (空行后) 业务规则检查
+        if (billing.Status == TenantBillingStatus.Paid)
+        {
+            throw new BusinessException(ErrorCodes.BusinessError, "已支付账单不允许重复收款");
+        }
+
+        if (billing.Status == TenantBillingStatus.Cancelled)
+        {
+            throw new BusinessException(ErrorCodes.BusinessError, "已取消账单不允许收款");
+        }
+
+        // 4. (空行后) 金额边界：不允许超过剩余应收（与前端校验保持一致）
+        var totalAmount = billing.CalculateTotalAmount();
+        var remainingAmount = totalAmount - billing.AmountPaid;
+        if (request.Amount > remainingAmount)
+        {
+            throw new BusinessException(ErrorCodes.BadRequest, "支付金额不能超过剩余应收");
+        }
+
+        // 5. (空行后) 幂等校验：交易号唯一
+        if (!string.IsNullOrWhiteSpace(request.TransactionNo))
+        {
+            var exists = await paymentRepository.GetByTransactionNoAsync(request.TransactionNo.Trim(), cancellationToken);
+            if (exists is not null)
+            {
+                throw new BusinessException(ErrorCodes.Conflict, "交易号已存在，疑似重复提交");
+            }
+        }
+
+        // 6. (空行后) 构建支付记录并立即审核通过
+        var now = DateTime.UtcNow;
+        var payment = new TenantPayment
+        {
+            Id = idGenerator.NextId(),
+            TenantId = billing.TenantId,
+            BillingStatementId = request.BillingId,
+            Amount = request.Amount,
+            Method = request.Method,
+            Status = TenantPaymentStatus.Pending,
+            TransactionNo = string.IsNullOrWhiteSpace(request.TransactionNo) ? null : request.TransactionNo.Trim(),
+            ProofUrl = request.ProofUrl,
+            PaidAt = now,
+            Notes = request.Notes
+        };
+
+        payment.Verify(currentUserAccessor.UserId);
+
+        // 7. (空行后) 同步更新账单已收金额/状态（支持分次收款）
+        billing.MarkAsPaid(payment.Amount, payment.TransactionNo ?? string.Empty);
+
+        // 8. (空行后) 持久化变更（同一 DbContext 下单次 SaveChanges 可提交两张表）
+        await paymentRepository.AddAsync(payment, cancellationToken);
+        await billingRepository.UpdateAsync(billing, cancellationToken);
+        await paymentRepository.SaveChangesAsync(cancellationToken);
+
+        // 9. (空行后) 返回 DTO
+        return payment.ToPaymentRecordDto();
+    }
+}
+