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  tracks are created unpublished.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- An unpublished track is only visible to its owner.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  unpublished totals.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

@@ -0,0 +1,6 @@
+namespace Musify.Application.Tracks.Responses
+{
+    public record SetTracksPublishedResponse(
+        IReadOnlyList<Guid> UpdatedTrackIds,
+        IReadOnlyList<Guid> SkippedTrackIds);
+}

backend/Core/Musify.Application/Tracks/Responses/TrackApplicationResponse.cs

@@ -14,7 +14,8 @@ namespace Musify.Application.Tracks.Responses
         DateTime UpdatedAt,
         long OwnerUserId,
         IReadOnlyCollection<Genre> Tags,
-        bool IsExplicit)
+        bool IsExplicit,
+        bool IsPublished)
     {
         public static TrackApplicationResponse FromEntity(Track track, int listensCount) =>
             new(
@@ -28,6 +29,7 @@ namespace Musify.Application.Tracks.Responses
                 track.UpdatedAt,
                 track.OwnerUserId,
                 track.Tags.Select(tag => tag.Tag).ToList(),
-                track.IsExplicit);
+                track.IsExplicit,
+                track.IsPublished);
     }
 }

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)

backend/Core/Musify.Application/Tracks/Responses/TrackStatusCountsResponse.cs

@@ -5,5 +5,7 @@ namespace Musify.Application.Tracks.Responses
         int Pending,
         int Processing,
         int Completed,
-        int Failed);
+        int Failed,
+        int Published,
+        int Unpublished);
 }

backend/Core/Musify.Application/Tracks/Responses/TrackUploadUrlsResponse.cs

@@ -1,16 +1,25 @@
 namespace Musify.Application.Tracks.Responses
 {
+    public record TrackAudioUpload(
+        Guid IntentId,
+        Guid? PictureIntentId,
+        string Key,
+        string Name,
+        string ContentType,
+        string UploadUrl);
+
     public record TrackUploadUrlsResponse(
-        Guid PictureIntentId,
+        Guid? PictureIntentId,
         Guid AudioIntentId,
         string Bucket,
-        string PictureKey,
-        string PictureName,
-        string PictureContentType,
-        string PictureUploadUrl,
+        string? PictureKey,
+        string? PictureName,
+        string? PictureContentType,
+        string? PictureUploadUrl,
         string AudioKey,
         string AudioName,
         string AudioContentType,
         string AudioUploadUrl,
-        int ExpiresInSeconds);
+        int ExpiresInSeconds,
+        IReadOnlyList<TrackAudioUpload> Audios);
 }

backend/Core/Musify.Application/Tracks/Responses/UserTrackApplicationResponse.cs

@@ -16,5 +16,6 @@ namespace Musify.Application.Tracks.Responses
         long OwnerUserId,
         IReadOnlyCollection<Genre> Tags,
         bool IsExplicit,
+        bool IsPublished,
         IReadOnlyList<TrackAlbumReference> Albums);
 }