fix(playlists): reject empty/whitespace name and description on update

backend/Musify.Api/Validators/PlayLists/UpdatePlayListRequestValidator.cs

@@ -8,10 +8,12 @@ public sealed class UpdatePlayListRequestValidator : AbstractValidator<UpdatePla
     public UpdatePlayListRequestValidator()
     {
         RuleFor(x => x.NewName)
+            .NotEmpty()
             .MaximumLength(50)
             .When(x => x.NewName is not null);
 
         RuleFor(x => x.NewDescription)
+            .NotEmpty()
             .MaximumLength(256)
             .When(x => x.NewDescription is not null);
     }

backend/Musify.Application/PlayLists/UpdatePlayList.cs

@@ -45,13 +45,13 @@ namespace Musify.Application.PlayLists
                 return Error.Unauthorized();
             }
 
-            if (request.NewName is not null)
+            if (!string.IsNullOrWhiteSpace(request.NewName))
             {
                 playListEntity.Name = request.NewName;
                 playListEntity.NormalizedName = request.NewName.Trim().ToUpperInvariant();
             }
 
-            if (request.NewDescription is not null)
+            if (!string.IsNullOrWhiteSpace(request.NewDescription))
             {
                 playListEntity.Description = request.NewDescription;
             }