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.Domain/Library/CollectionItem.cs

@@ -0,0 +1,25 @@
+namespace TeleWave.Domain.Library;
+
+/// <summary>Шоу в составе коллекции. Порядок показа — по <see cref="Position"/>.</summary>
+public class CollectionItem
+{
+    public Guid Id { get; private set; }
+    public Guid CollectionId { get; private set; }
+    public Guid ShowId { get; private set; }
+
+    /// <summary>Порядковый номер внутри коллекции (может иметь разрывы после удалений).</summary>
+    public int Position { get; private set; }
+
+    private CollectionItem() { }
+
+    internal static CollectionItem Create(Guid collectionId, Guid showId, int position) =>
+        new()
+        {
+            Id = Guid.NewGuid(),
+            CollectionId = collectionId,
+            ShowId = showId,
+            Position = position,
+        };
+
+    internal void SetPosition(int position) => Position = position;
+}