Implement billing functionality and enhance role management

- Introduced billing capabilities, allowing users to request payments for subscription periods (3/6/12 months) with admin approval via Telegram.
- Updated role management to include a `BillingEnabled` property, preventing billing for admin roles.
- Enhanced the `CreateRoleCommand` and `UpdateRoleCommand` to accept billing parameters, ensuring proper handling during role creation and updates.
- Added new endpoints for billing management and integrated billing checks into VPN config creation to enforce payment requirements.
- Updated related services, models, and tests to support the new billing features, ensuring comprehensive coverage and functionality.
- Enhanced documentation to reflect the new billing processes and role management changes.

backend/tests/PnvPanel.Application.Tests/Billing/GetMyBillingStatus/GetMyBillingStatusQueryHandlerTests.cs

@@ -0,0 +1,85 @@
+using NSubstitute;
+using PnvPanel.Application.Billing.GetMyBillingStatus;
+using PnvPanel.Application.Common.Interfaces;
+using PnvPanel.Application.Tests.TestSupport;
+using PnvPanel.Domain.Billing;
+using Xunit;
+
+namespace PnvPanel.Application.Tests.Billing.GetMyBillingStatus;
+
+public class GetMyBillingStatusQueryHandlerTests
+{
+    private readonly IIdentityService _identityService = Substitute.For<IIdentityService>();
+
+    private static CurrentUserProfile Profile(
+        Guid userId,
+        bool billingEnabled,
+        DateTimeOffset? paidUntil = null,
+        bool suspended = false
+    ) =>
+        new(
+            userId,
+            "alice",
+            Guid.NewGuid(),
+            "premium",
+            IsActivated: true,
+            IsBlocked: false,
+            MaxConfigs: 5,
+            MaxIpLimit: 3,
+            SubscriptionToken: "sub-token",
+            BillingEnabled: billingEnabled,
+            BillingPaidUntil: paidUntil,
+            BillingSuspended: suspended
+        );
+
+    [Fact]
+    public async Task Handle_WhenBillingNotEnabled_ReturnsDisabledStatusWithoutQueryingRequests()
+    {
+        using var dbContext = InMemoryDbContextFactory.Create();
+        var userId = Guid.NewGuid();
+        _identityService
+            .GetProfileAsync(userId, Arg.Any<CancellationToken>())
+            .Returns(Profile(userId, billingEnabled: false));
+
+        var handler = new GetMyBillingStatusQueryHandler(
+            dbContext,
+            _identityService,
+            FakeCurrentUser.Authenticated(userId)
+        );
+
+        var result = await handler.Handle(new GetMyBillingStatusQuery(), CancellationToken.None);
+
+        Assert.True(result.IsSuccess);
+        Assert.False(result.Value.BillingEnabled);
+        Assert.Null(result.Value.ActiveRequest);
+    }
+
+    [Fact]
+    public async Task Handle_WhenActiveRequestExists_IncludesItInStatus()
+    {
+        using var dbContext = InMemoryDbContextFactory.Create();
+        var userId = Guid.NewGuid();
+        var paidUntil = DateTimeOffset.UtcNow.AddDays(10);
+        var request = PaymentRequest.Create(userId, PaymentPeriod.Quarter, 1500);
+        dbContext.PaymentRequests.Add(request);
+        await dbContext.SaveChangesAsync(CancellationToken.None);
+
+        _identityService
+            .GetProfileAsync(userId, Arg.Any<CancellationToken>())
+            .Returns(Profile(userId, billingEnabled: true, paidUntil: paidUntil));
+
+        var handler = new GetMyBillingStatusQueryHandler(
+            dbContext,
+            _identityService,
+            FakeCurrentUser.Authenticated(userId)
+        );
+
+        var result = await handler.Handle(new GetMyBillingStatusQuery(), CancellationToken.None);
+
+        Assert.True(result.IsSuccess);
+        Assert.True(result.Value.BillingEnabled);
+        Assert.Equal(paidUntil, result.Value.PaidUntil);
+        Assert.NotNull(result.Value.ActiveRequest);
+        Assert.Equal(request.Id, result.Value.ActiveRequest!.Id);
+    }
+}