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  tracks are created unpublished.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- An unpublished track is only visible to its owner.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  unpublished totals.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/Tracks/Responses/TrackProjections.cs

@@ -8,6 +8,12 @@ namespace Musify.Application.Tracks.Responses
         public static IQueryable<Track> Active(this IQueryable<Track> query) =>
             query.Where(track => track.LifeCycleStatus == LifeCycleStatus.Active);
 
+        public static IQueryable<Track> WherePublished(this IQueryable<Track> query) =>
+            query.Where(track => track.IsPublished);
+
+        public static IQueryable<Track> VisibleTo(this IQueryable<Track> query, long? viewerId) =>
+            query.Where(track => track.IsPublished || track.OwnerUserId == viewerId);
+
         public static IQueryable<TrackApplicationResponse> SelectResponse(this IQueryable<Track> query) =>
             query.Select(track => new TrackApplicationResponse(
                 track.Id,
@@ -20,7 +26,8 @@ namespace Musify.Application.Tracks.Responses
                 track.UpdatedAt,
                 track.OwnerUserId,
                 track.Tags.Select(tag => tag.Tag).ToList(),
-                track.IsExplicit));
+                track.IsExplicit,
+                track.IsPublished));
 
         public static IQueryable<UserTrackApplicationResponse> SelectUserResponse(this IQueryable<Track> query) =>
             query.Select(track => new UserTrackApplicationResponse(
@@ -35,6 +42,7 @@ namespace Musify.Application.Tracks.Responses
                 track.OwnerUserId,
                 track.Tags.Select(tag => tag.Tag).ToList(),
                 track.IsExplicit,
+                track.IsPublished,
                 track.AlbumTracks
                     .Where(albumTrack => albumTrack.Album.LifeCycleStatus == LifeCycleStatus.Active)
                     .OrderBy(albumTrack => albumTrack.AddedAt)