refactor(infra): auto-configure MassTransit endpoints via ConfigureEndpoints

Replace ~240 lines of hand-written per-endpoint wiring with MassTransit's
ConfigureEndpoints + KebabCaseEndpointNameFormatter, and apply retry + EF
outbox globally through AddConfigureEndpointsCallback. Adding a consumer or
activity is now a single AddConsumer/AddActivity line.

- Normalize the 4 mismatched activity endpoint names to kebab-case so the
  routing-slip addressing keeps resolving (update-play-list-picture,
  delete/mark/publish play-list variants); cleanup consumer queue is now
  routing-slip-clean-up
- Drop the now-unused QueueName consts from event consumers and trim
  EndpointHelper / delete the manual endpoint-config partial

Verified end-to-end: booted the Worker against RabbitMQ in Docker and
confirmed all 38 endpoints are configured with the exact names the builders
address (19 execute queues + compensations + consumers + routing-slip-clean-up).

Build: 0 warnings, 0 errors.

backend/Musify.Infrastructure/MassTransit/Consumers/CreatePlayListConsumer.cs

@@ -9,7 +9,6 @@ namespace Musify.Infrastructure.MassTransit.Consumers
         PlayListPictureSourceRoutingSlipBuilder routingSlipBuilder)
         : IConsumer<CreatePlayListResourcesEvent>
     {
-        public const string QueueName = "create-playList";
 
         public async Task Consume(ConsumeContext<CreatePlayListResourcesEvent> consumeContext)
         {

backend/Musify.Infrastructure/MassTransit/Consumers/CreateTrackConsumer.cs

@@ -9,7 +9,6 @@ namespace Musify.Infrastructure.MassTransit.Consumers
         CreateTrackRoutingSlipBuilder routingSlipBuilder)
         : IConsumer<CreateTrackResourcesEvent>
     {
-        public const string QueueName = "create-track";
 
         public async Task Consume(ConsumeContext<CreateTrackResourcesEvent> consumeContext)
         {

backend/Musify.Infrastructure/MassTransit/Consumers/DeletePlayListConsumer.cs

@@ -9,7 +9,6 @@ namespace Musify.Infrastructure.MassTransit.Consumers
         DeletePlayListRoutingSlipBuilder routingSlipBuilder)
         : IConsumer<DeletePlayListEvent>
     {
-        public const string QueueName = "delete-playList";
 
         public async Task Consume(ConsumeContext<DeletePlayListEvent> consumeContext)
         {

backend/Musify.Infrastructure/MassTransit/Consumers/DeleteTrackConsumer.cs

@@ -9,7 +9,6 @@ namespace Musify.Infrastructure.MassTransit.Consumers
         DeleteTrackRoutingSlipBuilder routingSlipBuilder)
         : IConsumer<DeleteTrackEvent>
     {
-        public const string QueueName = "delete-track";
 
         public async Task Consume(ConsumeContext<DeleteTrackEvent> consumeContext)
         {

backend/Musify.Infrastructure/MassTransit/Consumers/EndpointHelper.cs

@@ -2,13 +2,7 @@ namespace Musify.Infrastructure.MassTransit.Consumers
 {
     internal static class EndpointHelper
     {
-        internal static string ExecuteQueueName(string endpointName) => $"{endpointName}_execute";
-
-        internal static string CompensateQueueName(string endpointName) => $"{endpointName}_compensate";
-
-        internal static Uri BuildExecuteActivityUri(string endpointName) => new($"queue:{ExecuteQueueName(endpointName)}");
-
-        internal static Uri BuildCompensateActivityUri(string endpointName) => new($"queue:{CompensateQueueName(endpointName)}");
+        internal static Uri BuildExecuteActivityUri(string endpointName) => new($"queue:{endpointName}_execute");
 
         internal static Uri BuildConsumerUri(string endpointName) => new($"queue:{endpointName}");
     }

backend/Musify.Infrastructure/MassTransit/Consumers/RoutingSlipCleanUpConsumer.cs

@@ -9,7 +9,7 @@ namespace Musify.Infrastructure.MassTransit.Consumers
         IConsumer<RoutingSlipCompleted>,
         IConsumer<RoutingSlipFaulted>
     {
-        public const string QueueName = "routing-slip-events";
+        public const string QueueName = "routing-slip-clean-up";
 
         public Task Consume(ConsumeContext<RoutingSlipCompleted> consumeContext)
             => DeleteFolder(consumeContext.Message.Variables);

backend/Musify.Infrastructure/MassTransit/Consumers/UpdatePlayListPictureConsumer.cs

@@ -9,7 +9,6 @@ namespace Musify.Infrastructure.MassTransit.Consumers
         PictureWorkflowRoutingSlipBuilder routingSlipBuilder)
         : IConsumer<UpdatePlayListPictureEvent>
     {
-        public const string QueueName = "update-playList-picture";
 
         public async Task Consume(ConsumeContext<UpdatePlayListPictureEvent> consumeContext)
         {

backend/Musify.Infrastructure/MassTransit/Consumers/UpdatePlayListPictureSourceConsumer.cs

@@ -9,7 +9,6 @@ namespace Musify.Infrastructure.MassTransit.Consumers
         PlayListPictureSourceRoutingSlipBuilder routingSlipBuilder)
         : IConsumer<UpdatePlayListPictureSourceEvent>
     {
-        public const string QueueName = "update-playList-picture-source";
 
         public async Task Consume(ConsumeContext<UpdatePlayListPictureSourceEvent> consumeContext)
         {

backend/Musify.Infrastructure/MassTransit/Consumers/UpdateTrackAudioConsumer.cs

@@ -9,7 +9,6 @@ namespace Musify.Infrastructure.MassTransit.Consumers
         AudioWorkflowRoutingSlipBuilder routingSlipBuilder)
         : IConsumer<UpdateTrackAudioEvent>
     {
-        public const string QueueName = "update-track-audio";
 
         public async Task Consume(ConsumeContext<UpdateTrackAudioEvent> consumeContext)
         {

backend/Musify.Infrastructure/MassTransit/Consumers/UpdateTrackPictureConsumer.cs

@@ -9,7 +9,6 @@ namespace Musify.Infrastructure.MassTransit.Consumers
         PictureWorkflowRoutingSlipBuilder routingSlipBuilder)
         : IConsumer<UpdateTrackPictureEvent>
     {
-        public const string QueueName = "update-track-picture";
 
         public async Task Consume(ConsumeContext<UpdateTrackPictureEvent> consumeContext)
         {