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/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);