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 Removed outdated bumper-related commands and handlers from the application, streamlining the codebase and improving maintainability.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/src/TeleWave.Application/Broadcast/Bumpers/UpdateBumperTemplateCommandHandler.cs

@@ -1,5 +1,4 @@
 using LiteCqrs;
-using Microsoft.EntityFrameworkCore;
 using TeleWave.Application.Common.Interfaces;
 using TeleWave.Application.Common.Models;
 
@@ -13,23 +12,15 @@ public sealed class UpdateBumperTemplateCommandHandler(IAppDbContext dbContext)
         CancellationToken cancellationToken
     )
     {
-        var channel = await dbContext
-            .Channels.Include(c => c.BumperTemplates)
-            .FirstOrDefaultAsync(c => c.Id == command.ChannelId, cancellationToken);
-        if (channel is null)
-            return Result.Failure(ChannelErrors.NotFound);
-
-        var template = channel.FindBumperTemplate(command.TemplateId);
-        if (template is null)
-            return Result.Failure(ChannelErrors.BumperTemplateNotFound);
-
-        template.UpdateStyle(
-            command.Name.Trim(),
-            command.BackgroundColor,
-            command.BackgroundColor2,
-            command.AccentColor,
-            command.TextColor
+        var template = await BumperTemplateLoader.LoadAsync(
+            dbContext,
+            command.TemplateId,
+            cancellationToken
         );
+        if (template is null)
+            return Result.Failure(BumperErrors.TemplateNotFound);
+
+        template.UpdateStyle(command.Style);
         return Result.Success();
     }
 }