Add margin-bottom to blog post images for spacing below hero images

Co-authored-by: grst <7051479+grst@users.noreply.github.com>
Agent-Logs-Url: https://github.com/scverse/scverse.github.io/sessions/480a99aa-b181-45ee-8179-85dc01e7a35a

Author: Copilot

assets/main.scss

@@ -940,6 +940,9 @@ body {
             margin: 3rem 0;
             font-size: 1.1rem;
             text-wrap: pretty;
+            img {
+                margin-bottom: 1.5rem;
+            }
             span.backticked {
                 font-size: 1.2rem;
                 line-height: 1.1rem;