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.Domain.Tests/Inbounds/InboundTests.cs

@@ -80,4 +80,42 @@ public class InboundTests
         Assert.False(inbound.IsAvailable);
         Assert.False(inbound.IsPublished);
     }
+
+    [Fact]
+    public void UpdateFromRemote_AfterMarkUnavailable_RestoresIsAvailable()
+    {
+        // Инбаунд пропадал с ноды, потом снова появился при следующей синхронизации — без сброса
+        // IsAvailable оставался бы недоступным навсегда, хотя реально снова опубликован на панели.
+        var inbound = Inbound.FromRemote(Guid.NewGuid(), "12", VpnProtocol.Vless, "Old", 443);
+        inbound.MarkUnavailable();
+
+        inbound.UpdateFromRemote(VpnProtocol.Vless, "New", 443);
+
+        Assert.True(inbound.IsAvailable);
+    }
+
+    [Fact]
+    public void Publish_AfterMarkUnavailable_RestoresIsAvailable()
+    {
+        var inbound = Inbound.FromRemote(Guid.NewGuid(), "12", VpnProtocol.Vless, "Germany", 443);
+        inbound.MarkUnavailable();
+
+        inbound.Publish("Germany", [Guid.NewGuid()]);
+
+        Assert.True(inbound.IsAvailable);
+    }
+
+    [Fact]
+    public void RemoveAllowedRole_RemovesOnlyMatchingRole()
+    {
+        var inbound = Inbound.FromRemote(Guid.NewGuid(), "12", VpnProtocol.Vless, "Germany", 443);
+        var roleId = Guid.NewGuid();
+        var otherRoleId = Guid.NewGuid();
+        inbound.Publish("Germany", [roleId, otherRoleId]);
+
+        inbound.RemoveAllowedRole(roleId);
+
+        Assert.DoesNotContain(roleId, inbound.AllowedRoleIds);
+        Assert.Contains(otherRoleId, inbound.AllowedRoleIds);
+    }
 }