fix: address PR review feedback on sitemap endpoint

- Remove LastModificationDate from root URL node (setting it to UtcNow on every cache expiry is an SEO anti-pattern; omitting it is cleaner than a stale value)
- Fix misleading startup comment: validation errors are logged and startup continues, not fail-fast
- Add test: GenerateSitemapXml_DoesNotIncludeSitemapRoute to prevent regression on sitemap self-listing filter

Author: BenjaminMichaelis

EssentialCSharp.Web.Tests/SitemapXmlHelpersTests.cs

@@ -187,6 +187,27 @@ public async Task GenerateSitemapXml_DoesNotIncludeErrorRoutes()
         await Assert.That(allUrls).DoesNotContain(url => url.Contains("/Error", StringComparison.OrdinalIgnoreCase));
     }
 
+    [Test]
+    public async Task GenerateSitemapXml_DoesNotIncludeSitemapRoute()
+    {
+        // Arrange
+        var siteMappings = new List<SiteMapping>();
+        var baseUrl = "https://test.example.com/";
+
+        // Act
+        var routeConfigurationService = _Factory.Services.GetRequiredService<IRouteConfigurationService>();
+        SitemapXmlHelpers.GenerateSitemapXml(
+            siteMappings,
+            routeConfigurationService,
+            baseUrl,
+            out var nodes);
+
+        var allUrls = nodes.Select(n => n.Url).ToList();
+
+        // /sitemap.xml should not list itself
+        await Assert.That(allUrls).DoesNotContain(url => url.Contains("sitemap", StringComparison.OrdinalIgnoreCase));
+    }
+
     [Test]
     public async Task GenerateSitemapXml_UsesLastModifiedDateFromSiteMapping()
     {

EssentialCSharp.Web/Helpers/SitemapXmlHelpers.cs

@@ -25,11 +25,10 @@ public static void GenerateSitemapXml(IEnumerable<SiteMapping> siteMappings, IRo
         // Routes should end up with leading slash
         baseUrl = baseUrl.TrimEnd('/');
 
-        // Start with the root URL
+        // Start with the root URL — no LastModificationDate: it doesn't change per-request
         nodes = new() {
             new($"{baseUrl}/")
             {
-                LastModificationDate = newDateTime,
                 ChangeFrequency = ChangeFrequency.Daily,
                 Priority = 1.0M
             }

EssentialCSharp.Web/Program.cs

@@ -571,7 +571,7 @@ await McpJsonRpcResponseWriter.WriteErrorAsync(
 
         app.MapFallbackToController("Index", "Home");
 
-        // Validate sitemap data at startup to fail fast on bad content
+        // Validate sitemap data at startup — logs errors but allows startup to continue
         var siteMappingService = app.Services.GetRequiredService<ISiteMappingService>();
         var logger = app.Services.GetRequiredService<ILogger<Program>>();