Rework post page (lead, pager), add skip link, unified focus ring, reduced motion and keyboard-accessible menu

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

@@ -23,6 +23,12 @@ public partial class MainLayout
     private IReadOnlyList<NavLinkItem> _header = [];
     private IReadOnlyList<NavLinkItem> _footer = [];
 
+    // The skip link's target on this very page: path and query of the request plus
+    // the fragment. See the comment on the skip link in the markup for why it cannot
+    // be a bare "#main".
+    private string SkipLinkHref =>
+        $"{HttpContext?.Request.PathBase}{HttpContext?.Request.Path}{HttpContext?.Request.QueryString}#main";
+
     // Berlin's year, not the server's (UTC) -- see FooterYear.
     private readonly int _year = FooterYear.For(TimeProvider.System.GetUtcNow());