feat(tracks): add user listening history

Record a listening-history entry when a stream ticket is issued and expose GET /users/{id}/listening-history to read it back.

backend/Musify.Domain/Entities/ListeningHistory.cs

@@ -0,0 +1,28 @@
+using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace Musify.Domain.Entities
+{
+#pragma warning disable CS8618
+    [Table("ListeningHistory")]
+    public class ListeningHistory
+    {
+        [Key]
+        public Guid Id { get; set; } = Guid.NewGuid();
+
+        [Required]
+        public required long UserId { get; set; }
+
+        [Required]
+        public required Guid TrackId { get; set; }
+
+        [Required]
+        public DateTime ListenedAt { get; set; } = DateTime.UtcNow;
+
+        [ForeignKey(nameof(UserId) )]
+        public User User { get; set; }
+
+        [ForeignKey(nameof(TrackId)) ]
+        public Track Track { get; set; }
+    }
+}