Add broadcast scheduling features: implement Show and Channel entities, enhance AppDbContext and DependencyInjection for broadcasting, and update API routing. Include migration for new database schema and update documentation for broadcast-related functionalities.

backend/src/TeleWave.Domain/Broadcast/ScheduleEntryKind.cs

@@ -0,0 +1,11 @@
+namespace TeleWave.Domain.Broadcast;
+
+/// <summary>Тип записи расписания.</summary>
+public enum ScheduleEntryKind
+{
+    /// <summary>Программа (серия шоу).</summary>
+    Program,
+
+    /// <summary>Рекламная врезка.</summary>
+    Ad,
+}