Auto-render first sample on page load

Uses app.load() to pre-render a random sample when the page opens,
so users see content immediately instead of an empty state.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app.py

@@ -410,6 +410,13 @@ def main():
             outputs=[plot_output, params_html, metrics_bar],
         )
 
+        # Auto-run first sample on page load
+        app.load(
+            fn=on_random_sample,
+            inputs=[field_dd],
+            outputs=[plot_output, params_html, metrics_bar],
+        )
+
     gr.Markdown(
         "<div style='text-align:center;padding:32px 0 8px;'>"
         "<span style='font-family:Inter,sans-serif;font-size:0.8rem;color:#6e6e6e;'>"