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  tracks are created unpublished.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- An unpublished track is only visible to its owner.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  unpublished totals.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/Core/Musify.Application/Pictures/GetCover.cs

@@ -35,10 +35,7 @@ namespace Musify.Application.Pictures
         {
             var (source, routes) = request.Owner switch
             {
-                CoverOwner.Track => (await database.Tracks.AsNoTracking()
-                    .Where(t => t.Id == request.Id && t.LifeCycleStatus == LifeCycleStatus.Active)
-                    .Select(t => new CoverSource(t.OwnerUserId, t.Pictures.OriginalName, t.Pictures.SmallName, t.Pictures.MediumName, t.Pictures.LargeName))
-                    .SingleOrDefaultAsync(cancellationToken), trackConfiguration.Routes),
+                CoverOwner.Track => await FindTrackSourceAsync(request.Id, cancellationToken),
                 CoverOwner.Album => (await database.Albums.AsNoTracking()
                     .Where(a => a.Id == request.Id && a.LifeCycleStatus == LifeCycleStatus.Active && a.Pictures != null)
                     .Select(a => new CoverSource(a.OwnerUserId, a.Pictures!.OriginalName, a.Pictures.SmallName, a.Pictures.MediumName, a.Pictures.LargeName))
@@ -71,5 +68,34 @@ namespace Musify.Application.Pictures
 
             return new CoverLocation(storageConfiguration.Bucket, key, MimeUtility.GetMimeMapping(name));
         }
+
+        private async Task<(CoverSource? Source, PictureRoutes Routes)> FindTrackSourceAsync(Guid trackId, CancellationToken cancellationToken)
+        {
+            var track = await database.Tracks.AsNoTracking()
+                .Where(t => t.Id == trackId && t.LifeCycleStatus == LifeCycleStatus.Active)
+                .Select(t => new
+                {
+                    Own = new CoverSource(t.OwnerUserId, t.Pictures.OriginalName, t.Pictures.SmallName, t.Pictures.MediumName, t.Pictures.LargeName),
+                    Album = t.AlbumTracks
+                        .Where(albumTrack => albumTrack.Album.LifeCycleStatus == LifeCycleStatus.Active && albumTrack.Album.Pictures != null)
+                        .OrderBy(albumTrack => albumTrack.AddedAt)
+                        .ThenBy(albumTrack => albumTrack.AlbumId)
+                        .Select(albumTrack => new CoverSource(
+                            albumTrack.Album.OwnerUserId,
+                            albumTrack.Album.Pictures!.OriginalName,
+                            albumTrack.Album.Pictures.SmallName,
+                            albumTrack.Album.Pictures.MediumName,
+                            albumTrack.Album.Pictures.LargeName))
+                        .FirstOrDefault()
+                })
+                .SingleOrDefaultAsync(cancellationToken);
+
+            if (track == null)
+                return (null, trackConfiguration.Routes);
+
+            return string.IsNullOrEmpty(track.Own.Original) && track.Album != null
+                ? (track.Album, albumConfiguration.Routes)
+                : (track.Own, trackConfiguration.Routes);
+        }
     }
 }