Implement billing status notification and enhance user management integration

- Added `NotifyBillingStatusChangedAsync` method to `IRealtimeNotifier` for notifying clients about changes in billing status.
- Updated `BillingConfigResumer` to call the new notification method after modifying billing configurations, ensuring users receive real-time updates.
- Enhanced `ListUsersQueryHandler` to include a `BillingPendingReview` property in `UserSummaryDto`, indicating if a user has a pending payment request awaiting confirmation.
- Refactored various command handlers to utilize `AdvisoryLock` for managing concurrent requests, preventing race conditions in billing operations.
- Updated tests to cover new notification behaviors and ensure proper functionality in billing status management.

backend/src/PnvPanel.Application/Billing/BillingConfigResumer.cs

@@ -60,6 +60,8 @@ public static class BillingConfigResumer
 
             config.SetBillingExpiry(newPaidUntil);
         }
+
+        await notifier.NotifyBillingStatusChangedAsync(userId, cancellationToken);
     }
 
     /// <summary>Заявка на оплату ждёт решения админа (AwaitingConfirmation) — держим клиента рабочим
@@ -71,6 +73,7 @@ public static class BillingConfigResumer
     public static async Task ProtectPendingConfigsAsync(
         IAppDbContext dbContext,
         IXuiPanelGateway gateway,
+        IRealtimeNotifier notifier,
         ILogger logger,
         Guid userId,
         CancellationToken cancellationToken
@@ -94,6 +97,8 @@ public static class BillingConfigResumer
                 cancellationToken
             );
         }
+
+        await notifier.NotifyBillingStatusChangedAsync(userId, cancellationToken);
     }
 
     /// <summary>Приостановка за неуплату — общая для фоновой джобы (BillingService) и немедленной
@@ -139,6 +144,8 @@ public static class BillingConfigResumer
                 cancellationToken
             );
         }
+
+        await notifier.NotifyBillingStatusChangedAsync(userId, cancellationToken);
     }
 
     private static Task<List<VpnConfig>> ActiveOrExpiredConfigsAsync(