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 Removed outdated bumper-related commands and handlers from the application, streamlining the codebase and improving maintainability.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.Domain.Tests/Broadcast/DomainRecordFactoryTests.cs

@@ -8,23 +8,20 @@ namespace TeleWave.Domain.Tests.Broadcast;
 public class DomainRecordFactoryTests
 {
     [Fact]
-    public void BumperAsset_Create_StoresPair()
+    public void BumperAsset_Create_StoresRenderedText()
     {
-        var channel = Guid.NewGuid();
         var template = Guid.NewGuid();
         var variant = Guid.NewGuid();
-        var from = Guid.NewGuid();
-        var to = Guid.NewGuid();
+        var poster = Guid.NewGuid();
         var asset = Guid.NewGuid();
 
-        var b = BumperAsset.Create(channel, template, variant, from, to, "sig", asset);
+        var b = BumperAsset.Create(template, variant, "sig", "[]", poster, asset);
 
-        Assert.Equal(channel, b.ChannelId);
         Assert.Equal(template, b.TemplateId);
         Assert.Equal(variant, b.VariantId);
-        Assert.Equal(from, b.FromShowId);
-        Assert.Equal(to, b.ToShowId);
         Assert.Equal("sig", b.Signature);
+        Assert.Equal("[]", b.RenderedLinesJson);
+        Assert.Equal(poster, b.PosterShowId);
         Assert.Equal(asset, b.MediaAssetId);
     }