Give the site a warm design system with card-based content lists

Elternbeirat.Web/Features/Posts/PostList.razor.css

@@ -1,20 +1,2 @@
-.post-list {
-    list-style: none;
-    padding: 0;
-}
-
-.post-list li {
-    padding: 0.75rem 0;
-    border-bottom: 1px solid #eee;
-}
-
-.post-list a {
-    font-size: 1.1rem;
-    text-decoration: none;
-}
-
-.post-list time {
-    display: block;
-    color: #777;
-    font-size: 0.85rem;
-}
+/* The .post-list card styles are shared with the home-page embed and live in the
+   global app.css. This page needs no extra styling of its own. */