Update scheduling parameters and refactor channel endpoints: extend HorizonDays to 7 and RetentionDays to 90 in appsettings.json. Consolidate channel-related endpoint logic by removing obsolete files and enhancing the ShowEndpoints with audience and genre management capabilities. Improve error handling and streamline command handlers for channel operations.

backend/src/TeleWave.Application/Library/Genres/CreateGenre/CreateGenreCommand.cs

@@ -0,0 +1,12 @@
+using LiteCqrs;
+using TeleWave.Application.Common.Models;
+
+namespace TeleWave.Application.Library.Genres.CreateGenre;
+
+/// <summary><paramref name="Aliases"/> — варианты написания для сопоставления с метаданными
+/// провайдеров; само название и ключ добавляются автоматически.</summary>
+public sealed record CreateGenreCommand(
+    string Name,
+    string Slug,
+    IReadOnlyList<string>? Aliases = null
+) : ICommand<Result<Guid>>;