dependencies and code cleanup (#2117)

* fix validation in new form layout

* pin mediatr to last oss version

* update dependencies

* cleanup code in core

* cleanup code in ffmpeg

* cleanup code in infra

* cleanup code in scanner

* cleanup code in application

* cleanup main code

* cleanup test code

* solution-wide code cleanup

ErsatzTV/ViewModels/DecoTemplateTreeItemViewModel.cs

@@ -1,6 +1,5 @@
 using ErsatzTV.Application.Scheduling;
 using MudBlazor;
-using S = System.Collections.Generic;
 
 namespace ErsatzTV.ViewModels;