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

Elternbeirat.Web.Tests/NavBuilderTests.cs

@@ -43,6 +43,15 @@ public class NavBuilderTests
         footer.Select(link => link.Title).ShouldBe(["Impressum", "Datenschutz"]);
     }
 
+    [Fact]
+    public void No_pages_give_empty_menus()
+    {
+        // PocketBase down or nothing published yet: both menus are empty lists, not
+        // null, so the layout can simply skip a column instead of crashing.
+        NavBuilder.Header([]).ShouldBeEmpty();
+        NavBuilder.Footer([]).ShouldBeEmpty();
+    }
+
     [Fact]
     public void Home_page_maps_to_root_every_other_slug_to_its_path()
     {