Add explicit flag to tracks and mark it on upload

backend/Core/Musify.Domain/Entities/Track.cs

@@ -31,6 +31,9 @@ namespace Musify.Domain.Entities
         [Required]
         public LifeCycleStatus LifeCycleStatus { get; set; } = LifeCycleStatus.Active;
 
+        [Required]
+        public bool IsExplicit { get; set; }
+
         [Required]
         public DateTime CreatedAt { get; set; } = DateTime.UtcNow;