Add post and event cards, shared calendar sheet and per-event ICS; rework past events and next-event card

Elternbeirat.Web/Features/Posts/PostList.razor

@@ -25,15 +25,12 @@ else if (_posts.Count == 0)
 }
 else
 {
-    <ul class="post-list">
-        @foreach (var post in _posts)
+    @* The newest post (GetPostsAsync sorts newest first) opens the page as a large
+       card across the full width; the rest follow in the grid. *@
+    <ul class="post-list post-list-grid">
+        @for (var i = 0; i < _posts.Count; i++)
         {
-            <li>
-                <a class="card-link" href="@($"/posts/{post.Slug}")">
-                    <span class="post-title">@post.Title</span>
-                    <PostDate Value="post.Date" />
-                </a>
-            </li>
+            <li class="@(i == 0 ? "post-list-featured" : null)"><PostCard Value="_posts[i]" Featured="i == 0" /></li>
         }
     </ul>
 }