Add bumper variant management: implement API endpoints for adding, updating, and removing bumper text variants, enhance data models to support variant details, and update scheduling logic to utilize variants. Refactor related components for improved bumper template handling and ensure proper error management for variant operations.

backend/src/TeleWave.Application/Broadcast/Bumpers/AddBumperTextVariantCommand.cs

@@ -0,0 +1,8 @@
+using LiteCqrs;
+using TeleWave.Application.Common.Models;
+
+namespace TeleWave.Application.Broadcast.Bumpers;
+
+/// <summary>Добавить подблок (текст-вариант) в блок заставки.</summary>
+public sealed record AddBumperTextVariantCommand(Guid ChannelId, Guid TemplateId, string Name)
+    : ICommand<Result<Guid>>;