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.Domain.Tests/Configs/VpnConfigTests.cs

@@ -137,6 +137,62 @@ public class VpnConfigTests
         Assert.Equal(ConfigStatus.Revoked, config.Status);
     }
 
+    [Fact]
+    public void Suspend_WhenActive_SetsExpired()
+    {
+        var config = VpnConfig.Create(Guid.NewGuid(), Guid.NewGuid(), VpnProtocol.Vless, null);
+
+        config.Suspend();
+
+        Assert.Equal(ConfigStatus.Expired, config.Status);
+    }
+
+    [Fact]
+    public void Suspend_WhenDisabledByAdmin_DoesNotOverrideBlock()
+    {
+        // Suspend (биллинг) не должен путать своё состояние с Disable (блокировка админом) — иначе
+        // Resume() ошибочно вернёт в Active конфиг, погашенный не за неуплату.
+        var config = VpnConfig.Create(Guid.NewGuid(), Guid.NewGuid(), VpnProtocol.Vless, null);
+        config.Disable();
+
+        config.Suspend();
+
+        Assert.Equal(ConfigStatus.Disabled, config.Status);
+    }
+
+    [Fact]
+    public void Resume_WhenExpired_ReturnsToActive()
+    {
+        var config = VpnConfig.Create(Guid.NewGuid(), Guid.NewGuid(), VpnProtocol.Vless, null);
+        config.Suspend();
+
+        config.Resume();
+
+        Assert.Equal(ConfigStatus.Active, config.Status);
+    }
+
+    [Fact]
+    public void Resume_WhenDisabledByAdmin_DoesNotResurrect()
+    {
+        var config = VpnConfig.Create(Guid.NewGuid(), Guid.NewGuid(), VpnProtocol.Vless, null);
+        config.Disable();
+
+        config.Resume();
+
+        Assert.Equal(ConfigStatus.Disabled, config.Status);
+    }
+
+    [Fact]
+    public void SetBillingExpiry_SetsExpiresAt()
+    {
+        var config = VpnConfig.Create(Guid.NewGuid(), Guid.NewGuid(), VpnProtocol.Vless, null);
+        var expiresAt = DateTimeOffset.UtcNow.AddMonths(3);
+
+        config.SetBillingExpiry(expiresAt);
+
+        Assert.Equal(expiresAt, config.ExpiresAt);
+    }
+
     [Fact]
     public void UpdateTraffic_SetsBytesAndLastSyncAt()
     {