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  tracks are created unpublished.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- An unpublished track is only visible to its owner.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  unpublished totals.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.Infrastructure/Persistence/Migrations/20260924231849_TrackPublicationAndAlbumType.cs

@@ -0,0 +1,42 @@
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace Musify.Infrastructure.Persistence.Migrations
+{
+    /// <inheritdoc />
+    public partial class TrackPublicationAndAlbumType : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.AddColumn<bool>(
+                name: "IsPublished",
+                table: "Tracks",
+                type: "boolean",
+                nullable: false,
+                defaultValue: false);
+
+            migrationBuilder.Sql("UPDATE \"Tracks\" SET \"IsPublished\" = TRUE;");
+
+            migrationBuilder.AddColumn<int>(
+                name: "Type",
+                table: "Albums",
+                type: "integer",
+                nullable: false,
+                defaultValue: 0);
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropColumn(
+                name: "IsPublished",
+                table: "Tracks");
+
+            migrationBuilder.DropColumn(
+                name: "Type",
+                table: "Albums");
+        }
+    }
+}

backend/Core/Musify.Infrastructure/Persistence/Migrations/DatabaseModelSnapshot.cs

@@ -224,6 +224,9 @@ namespace Musify.Infrastructure.Persistence.Migrations
                         .HasMaxLength(200)
                         .HasColumnType("character varying(200)");
 
+                    b.Property<int>("Type")
+                        .HasColumnType("integer");
+
                     b.Property<DateTime>("UpdatedAt")
                         .HasColumnType("timestamp with time zone");
 
@@ -435,6 +438,9 @@ namespace Musify.Infrastructure.Persistence.Migrations
                     b.Property<bool>("IsExplicit")
                         .HasColumnType("boolean");
 
+                    b.Property<bool>("IsPublished")
+                        .HasColumnType("boolean");
+
                     b.Property<int>("LifeCycleStatus")
                         .HasColumnType("integer");