Implement extension request and gift functionalities in billing system

- Added new endpoints for creating and managing extension requests, allowing users to request billing period extensions.
- Implemented admin approval processes for extension requests via Telegram, including inline buttons for approval and rejection.
- Introduced a gifting feature for admins to grant additional billing days directly to users without a request.
- Updated the support ticket model to accommodate extension requests and their associated properties.
- Enhanced the Telegram notifier to inform admins of new extension requests and notify users of approval or rejection.
- Updated frontend components to support the new extension request and gifting functionalities, including user interfaces for managing these features.
- Revised API documentation to reflect the new endpoints and their usage in the billing context.

backend/tests/PnvPanel.Application.Tests/Support/CreateExtensionRequestTicketCommandHandlerTests.cs

@@ -0,0 +1,124 @@
+using NSubstitute;
+using PnvPanel.Application.Billing;
+using PnvPanel.Application.Common.Interfaces;
+using PnvPanel.Application.Support;
+using PnvPanel.Application.Support.CreateExtensionRequest;
+using PnvPanel.Application.Tests.TestSupport;
+using PnvPanel.Domain.Support;
+using Xunit;
+
+namespace PnvPanel.Application.Tests.Support;
+
+public class CreateExtensionRequestTicketCommandHandlerTests
+{
+    private readonly IIdentityService _identityService = Substitute.For<IIdentityService>();
+    private readonly IRealtimeNotifier _notifier = Substitute.For<IRealtimeNotifier>();
+    private readonly ITelegramNotifier _telegramNotifier = Substitute.For<ITelegramNotifier>();
+
+    private static CurrentUserProfile Profile(Guid userId, bool billingEnabled) =>
+        new(
+            userId,
+            "alice",
+            Guid.NewGuid(),
+            "premium",
+            IsActivated: true,
+            IsBlocked: false,
+            MaxConfigs: 5,
+            MaxIpLimit: 3,
+            SubscriptionToken: "sub-token",
+            BillingEnabled: billingEnabled,
+            BillingPaidUntil: null,
+            BillingSuspended: false
+        );
+
+    [Fact]
+    public async Task Handle_WhenBillingEnabled_CreatesTicketAndNotifiesAdmins()
+    {
+        using var dbContext = InMemoryDbContextFactory.Create();
+        var userId = Guid.NewGuid();
+        _identityService
+            .GetProfileAsync(userId, Arg.Any<CancellationToken>())
+            .Returns(Profile(userId, billingEnabled: true));
+
+        var handler = new CreateExtensionRequestTicketCommandHandler(
+            dbContext,
+            _identityService,
+            _notifier,
+            _telegramNotifier,
+            FakeCurrentUser.Authenticated(userId, "alice")
+        );
+
+        var result = await handler.Handle(
+            new CreateExtensionRequestTicketCommand(14, "нужно продлить"),
+            CancellationToken.None
+        );
+
+        Assert.True(result.IsSuccess);
+        Assert.Equal(TicketType.ExtensionRequest, result.Value.Type);
+        Assert.Equal(14, result.Value.RequestedDays);
+        await _telegramNotifier
+            .Received(1)
+            .NotifyAdminsExtensionRequestCreatedAsync(
+                Arg.Any<Guid>(),
+                "alice",
+                14,
+                "нужно продлить",
+                Arg.Any<CancellationToken>()
+            );
+    }
+
+    [Fact]
+    public async Task Handle_WhenBillingNotEnabled_ReturnsNotEnabled()
+    {
+        using var dbContext = InMemoryDbContextFactory.Create();
+        var userId = Guid.NewGuid();
+        _identityService
+            .GetProfileAsync(userId, Arg.Any<CancellationToken>())
+            .Returns(Profile(userId, billingEnabled: false));
+
+        var handler = new CreateExtensionRequestTicketCommandHandler(
+            dbContext,
+            _identityService,
+            _notifier,
+            _telegramNotifier,
+            FakeCurrentUser.Authenticated(userId)
+        );
+
+        var result = await handler.Handle(
+            new CreateExtensionRequestTicketCommand(14, "нужно продлить"),
+            CancellationToken.None
+        );
+
+        Assert.False(result.IsSuccess);
+        Assert.Equal(BillingErrors.NotEnabled, result.Error);
+    }
+
+    [Fact]
+    public async Task Handle_WhenPendingExtensionRequestExists_ReturnsConflict()
+    {
+        using var dbContext = InMemoryDbContextFactory.Create();
+        var userId = Guid.NewGuid();
+        dbContext.SupportTickets.Add(SupportTicket.CreateExtensionRequest(userId, 7));
+        await dbContext.SaveChangesAsync(CancellationToken.None);
+
+        _identityService
+            .GetProfileAsync(userId, Arg.Any<CancellationToken>())
+            .Returns(Profile(userId, billingEnabled: true));
+
+        var handler = new CreateExtensionRequestTicketCommandHandler(
+            dbContext,
+            _identityService,
+            _notifier,
+            _telegramNotifier,
+            FakeCurrentUser.Authenticated(userId)
+        );
+
+        var result = await handler.Handle(
+            new CreateExtensionRequestTicketCommand(3, "ещё заявка"),
+            CancellationToken.None
+        );
+
+        Assert.False(result.IsSuccess);
+        Assert.Equal(SupportErrors.ExtensionRequestAlreadyPending, result.Error);
+    }
+}