Fix very wide images overflowing posts horizontally (#39812)

app/javascript/styles/mastodon/components.scss

@@ -7255,6 +7255,7 @@ a.status-card {
   border-radius: 8px;
   position: relative;
   width: 100%;
+  max-width: 100%;
   min-height: 64px;
   display: grid;
   grid-template-columns: 1fr 1fr;