Lay out stat cards as 2 per row (3 rows)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/components/datasets/protein/StatsPanel.css

@@ -1,6 +1,6 @@
 .stats-panel {
   display: grid;
-  grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
+  grid-template-columns: repeat(2, 1fr);
   gap: 15px;
   padding: 0;
 }