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.Api/Program.cs

@@ -113,6 +113,8 @@ app.MapAuthEndpoints();
 app.MapRoleEndpoints();
 app.MapAdminUserEndpoints();
 app.MapMediaEndpoints();
+app.MapShowEndpoints();
+app.MapChannelEndpoints();
 
 // Раздача статики SPA из wwwroot + fallback на index.html для клиентских маршрутов.
 app.UseDefaultFiles();