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/tests/PnvPanel.Application.Tests/Support/ReopenTicketCommandHandlerTests.cs

@@ -83,4 +83,29 @@ public class ReopenTicketCommandHandlerTests
         Assert.False(result.IsSuccess);
         Assert.Equal(SupportErrors.NotFound, result.Error);
     }
+
+    [Fact]
+    public async Task Handle_WhenRoleRequestResolved_ReturnsOnlyBugReportCanBeReopened()
+    {
+        // approve/reject — единственный способ решить заявку на роль/продление (см. CLAUDE.md);
+        // Reopen для них запрещён даже если тикет каким-то образом оказался Resolved.
+        using var dbContext = InMemoryDbContextFactory.Create();
+        var userId = Guid.NewGuid();
+        var ticket = SupportTicket.CreateRoleRequestForExistingRole(userId, Guid.NewGuid());
+        ticket.Resolve();
+        dbContext.SupportTickets.Add(ticket);
+        await dbContext.SaveChangesAsync(CancellationToken.None);
+
+        var currentUser = FakeCurrentUser.Authenticated(userId);
+        var handler = new ReopenTicketCommandHandler(dbContext, _telegramNotifier, currentUser);
+
+        var result = await handler.Handle(
+            new ReopenTicketCommand(ticket.Id),
+            CancellationToken.None
+        );
+
+        Assert.False(result.IsSuccess);
+        Assert.Equal(SupportErrors.OnlyBugReportCanBeReopened, result.Error);
+        Assert.Equal(TicketStatus.Resolved, ticket.Status);
+    }
 }