Refresh header and footer with signet, gradient, nav pills and three-column footer; fix box-sizing of design boxes

Elternbeirat.Web/Components/Layout/MainLayout.razor.cs

@@ -23,6 +23,9 @@ public partial class MainLayout
     private IReadOnlyList<NavLinkItem> _header = [];
     private IReadOnlyList<NavLinkItem> _footer = [];
 
+    // Berlin's year, not the server's (UTC) -- see FooterYear.
+    private readonly int _year = FooterYear.For(TimeProvider.System.GetUtcNow());
+
     protected override async Task OnInitializedAsync()
     {
         try