Implement BumperEndpoints and remove deprecated bumper-related functionality

Added new BumperEndpoints to the API for managing bumper templates and variants, enhancing the channel management capabilities. Removed outdated bumper-related commands and handlers from the application, streamlining the codebase and improving maintainability. Updated ChannelEndpoints to reflect these changes and ensure proper routing for the new endpoints.

backend/tests/TeleWave.Application.Tests/Streaming/ListPublicChannelsTests.cs

@@ -31,8 +31,8 @@ public class ListPublicChannelsTests
         var disabled = Channel.Create("Выключенный", "off", T0);
 
         foreach (var channel in new[] { numbered, first, unnumbered })
-            channel.UpdateSettings(channel.Name, isEnabled: true, bumpersEnabled: false, null);
-        disabled.UpdateSettings("Выключенный", isEnabled: false, bumpersEnabled: false, null);
+            channel.UpdateSettings(channel.Name, isEnabled: true, null);
+        disabled.UpdateSettings("Выключенный", isEnabled: false, null);
 
         await using (var seed = fixture.New())
         {
@@ -57,7 +57,7 @@ public class ListPublicChannelsTests
     {
         var fixture = new TestDb();
         var channel = Channel.Create("Первый", "one", T0);
-        channel.UpdateSettings("Первый", isEnabled: true, bumpersEnabled: false, null);
+        channel.UpdateSettings("Первый", isEnabled: true, null);
         var logoId = Guid.NewGuid();
         channel.UpdateViewerSettings(logoId, LogoCorner.TopRight, 0.5, showClock: true, 0.3);