Add track publication, album types, optional track pictures and batch upload URLs

Tracks
- Track.IsPublished (migration marks existing tracks as published). New
  tracks are created unpublished.
- PUT /tracks/{id}/published and PUT /tracks/published change the flag;
  publishing requires completed audio processing (the batch endpoint
  reports skipped tracks).
- An unpublished track is only visible to its owner. A WherePublished /
  VisibleTo filter is applied to search, genres, listening history, last
  listened, likes, mixes, album and playlist contents and counts, recently
  listened albums, public user tracks, track details and stream tickets.
- isPublished is part of the track responses, GET /tracks/users/{userId}
  accepts a published filter and status-counts reports published and
  unpublished totals.
- CreateTrackRequest.pictureIntentId is optional: without it the track
  uses the album cover or the preset picture and no picture processing
  runs. CreateTrackResourcesEvent carries nullable picture fields, so
  queues must be drained before deploying.
- POST /tracks/upload-urls accepts an audios list and one optional picture
  shared by all of them, and returns an intent per file. The upload intent
  limits are raised so a batch fits.

Albums
- AlbumType (Album, EP, Single) on create, update and responses.
- CreateAlbumRequest.trackIds creates the album and links the tracks in a
  single save.

backend/Tests/Musify.Infrastructure.Tests/MassTransit/ProcessingStateMachineTests.cs

@@ -33,6 +33,24 @@ namespace Musify.Infrastructure.Tests.MassTransit
             Assert.False(await harness.Published.Any<TrackProcessingFailed>(Ct));
         }
 
+        [Fact]
+        public async Task Track_WithoutPicture_CompletesOnceTheAudioIsProcessed()
+        {
+            await using var provider = CreateProvider<TrackProcessingStateMachine, TrackProcessingState>();
+            var harness = await StartAsync(provider);
+            var saga = provider.GetRequiredService<ISagaStateMachineTestHarness<TrackProcessingStateMachine, TrackProcessingState>>();
+            var id = Guid.NewGuid();
+
+            await harness.Bus.Publish(
+                new CreateTrackResourcesEvent(id, null, Guid.NewGuid(), "bucket", null, null, "audio-source", "audio", "audio-folder", Sizes), Ct);
+            Assert.NotNull(await saga.Exists(id, machine => machine.Processing));
+
+            await harness.Bus.Publish(new TrackAudioProcessed(id), Ct);
+
+            Assert.Null(await saga.NotExists(id));
+            Assert.False(await harness.Published.Any<TrackProcessingFailed>(Ct));
+        }
+
         [Fact]
         public async Task Track_PictureFailed_PublishesProcessingFailedAndMovesToFailed()
         {