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  tracks are created unpublished.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- An unpublished track is only visible to its owner.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  unpublished totals.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/Mixes/MixItemMapper.cs

@@ -9,6 +9,22 @@ namespace Musify.Application.Mixes
 
     internal static class MixItemMapper
     {
+        public static async Task<HashSet<Guid>> VisibleTrackIdsAsync(
+            IDatabase database,
+            IEnumerable<MixItem> items,
+            CancellationToken cancellationToken)
+        {
+            var trackIds = items.Select(item => item.TrackId).Distinct().ToList();
+
+            var visible = await database.Tracks
+                .AsNoTracking()
+                .Where(track => trackIds.Contains(track.Id) && track.LifeCycleStatus == LifeCycleStatus.Active && track.IsPublished)
+                .Select(track => track.Id)
+                .ToListAsync(cancellationToken);
+
+            return [.. visible];
+        }
+
         public static async Task<List<MixItemApplicationResponse>> ToResponsesAsync(
             IDatabase database,
             IReadOnlyList<MixItem> orderedItems,
@@ -19,7 +35,7 @@ namespace Musify.Application.Mixes
             var tracksById = await database.Tracks
                 .AsNoTracking()
                 .Include(track => track.Owner)
-                .Where(track => trackIds.Contains(track.Id) && track.LifeCycleStatus == LifeCycleStatus.Active)
+                .Where(track => trackIds.Contains(track.Id) && track.LifeCycleStatus == LifeCycleStatus.Active && track.IsPublished)
                 .Select(track => new { Track = track, ListensCount = track.ListeningHistories.Count(l => l.IsCounted) })
                 .ToDictionaryAsync(x => x.Track.Id, cancellationToken);