Enhance user plan management and update related endpoints

- Added new configuration options for user plans in `.env.example`, including `Plans__MaxCustomConfigCount` and `Plans__MinCustomConfigCount`.
- Introduced `MapPlanEndpoints` in `Program.cs` to handle plan-related API routes.
- Implemented `SetUserPlan` endpoint in `RoleEndpoints` to allow admins to assign plans to users.
- Removed deprecated role request approval endpoints from `AdminSupportEndpoints`.
- Updated `ITelegramNotifier` and related classes to reflect changes in role request handling and payment notifications.
- Refactored role management commands to remove `MaxConfigs` and focus on `MaxIpLimit` and billing settings.
- Enhanced billing request handling to accommodate plan changes instead of role changes.
- Updated various interfaces and command handlers to support new plan management features.

backend/src/PnvPanel.Application/Plans/ChangePlanCommand.cs

@@ -0,0 +1,16 @@
+using PnvPanel.Application.Common.Messaging;
+using PnvPanel.Application.Common.Models;
+
+namespace PnvPanel.Application.Plans;
+
+/// <summary>Ровно одно из PlanId/CustomConfigCount задано. ConfigIdsToRevoke обязателен и должен
+/// содержать ровно (текущее число конфигов, занимающих квоту (Active + Expired) - новая квота) id,
+/// если новая квота меньше этого числа — самостоятельное понижение тарифа требует явного выбора,
+/// какие конфиги отозвать, а не молчаливый грандфазеринг (см. ChangePlanCommandHandler).</summary>
+public sealed record ChangePlanCommand(
+    Guid? PlanId,
+    int? CustomConfigCount,
+    IReadOnlyList<Guid> ConfigIdsToRevoke
+) : ICommand<Result<ChangePlanResultDto>>, IRequiresActivation;
+
+public sealed record ChangePlanResultDto(int ConfigQuota, Guid? PlanId, int? TopUpAmount);