nav: highlight active page with active class and aria-current

Add PageHelpers.ActivePage extension and apply it to top-level nav
items and the Account/Register + Account/Signin items in _LoginPartial,
so the current route gets the active class and aria-current="page"
for accessibility.

src/Yavsc.Org/Helpers/PageHelpers.cs

@@ -1,12 +1,51 @@
 using System;
 using System.Collections.Generic;
+using Microsoft.AspNetCore.Html;
 using Microsoft.AspNetCore.Mvc.Rendering;
+using Microsoft.AspNetCore.Mvc.ViewFeatures;
 using Microsoft.Extensions.Localization;
 
 namespace Yavsc.Server.Helpers
 {
     public static class PageHelpers
     {
+        /// <summary>
+        /// Returns "active" aria-current="page" when the current route matches the given
+        /// controller/action, otherwise an empty string. Use as an attribute value
+        /// inside a &lt;a class="nav-link @..."&gt; element.
+        /// Pass an empty controller (or "Home" with action "Index") to match the site root.
+        /// </summary>
+        public static IHtmlContent ActivePage(this ViewContext viewContext, string controller, string action = null)
+        {
+            var route = viewContext?.RouteData.Values;
+            if (route == null) return HtmlString.Empty;
+
+            var currentController = route["controller"] as string;
+            var currentAction = route["action"] as string;
+
+            // Normalize: empty or "Home" + ("Index" or null) both target the site root.
+            bool isHome = string.IsNullOrEmpty(controller)
+                || (string.Equals(controller, "Home", StringComparison.Ordinal)
+                    && (action == null || string.Equals(action, "Index", StringComparison.Ordinal)));
+
+            bool isCurrent;
+            if (isHome)
+            {
+                isCurrent = string.IsNullOrEmpty(currentController)
+                    || string.Equals(currentController, "Home", StringComparison.Ordinal)
+                        && (currentAction == null || string.Equals(currentAction, "Index", StringComparison.Ordinal));
+            }
+            else
+            {
+                isCurrent = string.Equals(currentController, controller, StringComparison.Ordinal)
+                    && (action == null || string.Equals(currentAction, action, StringComparison.Ordinal));
+            }
+
+            return isCurrent
+                ? (IHtmlContent)new HtmlString("active\" aria-current=\"page")
+                : HtmlString.Empty;
+        }
+
         public static List<SelectListItem> CreateSelectListItems<T> (this IStringLocalizer<T>  localisation, Type enumType, object selectedValue =null)
         {
             string selectedName = (selectedValue != null) ? enumType.GetEnumName(selectedValue) : null;

src/Yavsc.Org/Views/Shared/_LoginPartial.cshtml

@@ -49,10 +49,10 @@
 else
 {
     <li class="dropdown-item">
-        <a class="nav-link" asp-controller="Account" asp-action="Register" >Register</a>
+        <a class="nav-link @PageHelpers.ActivePage(ViewContext, "Account", "Register")" asp-controller="Account" asp-action="Register" >Register</a>
     </li>
     <li class="dropdown-item">
-        <a class="nav-link" asp-controller="Account" asp-action="Signin" asp-route-ReturnUrl="~/" asp-route-AllowRememberLogin="true" >Signin</a>
+        <a class="nav-link @PageHelpers.ActivePage(ViewContext, "Account", "Signin")" asp-controller="Account" asp-action="Signin" asp-route-ReturnUrl="~/" asp-route-AllowRememberLogin="true" >Signin</a>
     </li>
 }
 

src/Yavsc.Org/Views/Shared/_Nav.cshtml

@@ -13,10 +13,10 @@ background-attachment: fixed;">
       </button>
       <div class="collapse navbar-collapse" id="navbar" >
         <ul class="navbar-nav me-auto" >
-          <li class="nav-item"><a class="nav-link active" aria-current="page" href="/">Home</a></li>
+          <li class="nav-item"><a class="nav-link @PageHelpers.ActivePage(ViewContext, "")" href="/">@Localizer["Home"]</a></li>
-          <li class="nav-item"><a asp-controller="Blogspot" asp-action="Index" class="nav-link">@Localizer["Blogs"]</a></li>
+          <li class="nav-item"><a asp-controller="Blogspot" asp-action="Index" class="nav-link @PageHelpers.ActivePage(ViewContext, "Blogspot")">@Localizer["Blogs"]</a></li>
-          <li class="nav-item"><a asp-controller="Home" asp-action="Contact" class="nav-link">@Localizer["Contact"]</a></li>
+          <li class="nav-item"><a asp-controller="Home" asp-action="Contact" class="nav-link @PageHelpers.ActivePage(ViewContext, "Home", "Contact")">@Localizer["Contact"]</a></li>
-          <li class="nav-item"><a asp-controller="Home" asp-action="About" class="nav-link">@Localizer["About"]</a></li>
+          <li class="nav-item"><a asp-controller="Home" asp-action="About" class="nav-link @PageHelpers.ActivePage(ViewContext, "Home", "About")">@Localizer["About"]</a></li>
           <partial name="_LoginPartial" />
         </ul>
       </div>