feat(infra): add Track processing saga (state machine, phase 1)

Introduce a MassTransit saga state machine that correlates by TrackId and
tracks the two parallel processing slips (picture + audio):
- TrackProcessingStateMachine + EF-persisted TrackProcessingState
  (pessimistic concurrency, EntityFrameworkRepository), migration added
- Starts on CreateTrackResourcesEvent; UpdateTrack{Picture,Audio}Activity now
  publish TrackPictureProcessed / TrackAudioProcessed on success; when both
  arrive the saga finalizes (Ready). Failure transitions to a Failed state
  (cleanup wired in the next phase)
- Add LifeCycleStatus.Failed and the four outcome events

Verified: booted the Worker against RabbitMQ + migrated Postgres in Docker;
the saga endpoint 'track-processing-state' is configured and the bus starts
clean.

Build: 0 warnings, 0 errors.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/Musify.Domain/ValueObjects/LifeCycleStatus.cs

@@ -3,6 +3,7 @@ namespace Musify.Domain.ValueObjects
     public enum LifeCycleStatus
     {
         Active = 0,
-        Removing = 1
+        Removing = 1,
+        Failed = 2
     }
 }