Add news post type with list and detail routes

Elternbeirat.Web/Components/Pages/PostDetail.razor

@@ -0,0 +1,46 @@
+@page "/beitraege/{Slug}"
+@using System.Globalization
+@using Elternbeirat.Web.Services
+@inject PostService PostService
+
+@if (_post is null)
+{
+    <PageTitle>Nicht gefunden</PageTitle>
+}
+else
+{
+    <PageTitle>@_post.Title</PageTitle>
+    <article>
+        <p class="post-meta">
+            <a href="/beitraege">&larr; Alle Beiträge</a>
+            <time datetime="@_post.Date.ToString("yyyy-MM-dd")">
+                @_post.Date.ToString("d. MMMM yyyy", _german)
+            </time>
+        </p>
+        @((MarkupString)_post.ContentHtml)
+    </article>
+}
+
+@code {
+    private static readonly CultureInfo _german = CultureInfo.GetCultureInfo("de-DE");
+
+    [Parameter]
+    public string Slug { get; set; } = "";
+
+    private Post? _post;
+
+    protected override void OnParametersSet()
+    {
+        _post = PostService.Find(Slug);
+
+        // Unknown slug -> 404, so UseStatusCodePagesWithReExecute serves the
+        // /not-found page instead of an empty 200 response.
+        if (_post is null && HttpContext is not null)
+        {
+            HttpContext.Response.StatusCode = StatusCodes.Status404NotFound;
+        }
+    }
+
+    [CascadingParameter]
+    private HttpContext? HttpContext { get; set; }
+}