chore: add documentation comments and stylecop rules

src/Application/TakeoutSaaS.Application/App/Tenants/Handlers/GetTenantBillQueryHandler.cs

@@ -13,7 +13,10 @@ public sealed class GetTenantBillQueryHandler(ITenantBillingRepository billingRe
 {
     public async Task<TenantBillingDto?> Handle(GetTenantBillQuery request, CancellationToken cancellationToken)
     {
+        // 1. 查询账单
         var bill = await billingRepository.FindByIdAsync(request.TenantId, request.BillingId, cancellationToken);
+
+        // 2. 返回 DTO 或 null
         return bill?.ToDto();
     }
 }