Restructure into feature folders with code-behind and scoped CSS

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

@@ -0,0 +1,13 @@
+.post-meta {
+    display: flex;
+    justify-content: space-between;
+    align-items: baseline;
+    gap: 1rem;
+    margin-bottom: 1rem;
+}
+
+.post-meta time {
+    display: block;
+    color: #777;
+    font-size: 0.85rem;
+}