ui: render validity_rate as percentage in the leaderboard table

Convert the 0-1 float into 'NN%' (or 'NN.N%' for non-whole values)
just before passing the table to gr.Dataframe, so the column reads as
'100%' instead of '1' / '1.0'. Underlying row schema is unchanged -
validity_rate is still stored as a float in [0, 1] in results.jsonl.

Side-effect: this column now sorts alphabetically rather than
numerically because gr.Dataframe sees strings. Acceptable for v1 - the
primary sort is aggregate_score and validity_rate hovers around 100%
for serious submissions anyway. If finer sorting matters later, switch
to a numeric column with a Gradio formatter.

Co-authored-by: Cursor <cursoragent@cursor.com>

app.py

@@ -67,6 +67,14 @@ def _load_rows_from_local() -> list[dict]:
     ]
 
 
+def _fmt_pct(x: float | None) -> str:
+    """Render a 0-1 fraction as 'NN%' (or 'NN.N%' for non-whole values)."""
+    if x is None:
+        return ""
+    pct = float(x) * 100
+    return f"{pct:.0f}%" if pct == int(pct) else f"{pct:.1f}%"
+
+
 def load_leaderboard() -> pd.DataFrame:
     rows = _load_rows_from_hub()
     if rows is None:
@@ -76,11 +84,14 @@ def load_leaderboard() -> pd.DataFrame:
         return pd.DataFrame(columns=LEADERBOARD_COLS)
     df = pd.DataFrame(rows)
     cols = [c for c in LEADERBOARD_COLS if c in df.columns]
-    return (
+    df = (
         df[cols]
         .sort_values("aggregate_score", ascending=False, na_position="last")
         .reset_index(drop=True)
     )
+    if "validity_rate" in df.columns:
+        df["validity_rate"] = df["validity_rate"].map(_fmt_pct)
+    return df
 
 
 def handle_submit(