fix: remove unnecessary f-string prefixes and unused import (#2352)

- Remove f-string prefix on 7 strings with no placeholders (F541)
  in analyze.py, aggregate_benchmark.py, run_loop.py, generate_review.py
- Remove unused `os` import in quick_validate.py (F401)

Found by ruff via HUMMBL Arbiter (https://hummbl.io/audit).

skills/public/data-analysis/scripts/analyze.py

@@ -215,14 +215,14 @@ def action_inspect(con: duckdb.DuckDBPyConnection, table_map: dict[str, str]) ->
         non_null_sql = f'SELECT {", ".join(non_null_parts)} FROM "{table_name}"'
         try:
             non_null_counts = con.execute(non_null_sql).fetchone()
-            output_parts.append(f"\nNon-null counts:")
+            output_parts.append("\nNon-null counts:")
             for i, c in enumerate(col_names):
                 output_parts.append(f"  {c}: {non_null_counts[i]} / {row_count}")
         except Exception:
             pass
 
         # Sample data (first 5 rows)
-        output_parts.append(f"\nSample data (first 5 rows):")
+        output_parts.append("\nSample data (first 5 rows):")
         try:
             sample = con.execute(f'SELECT * FROM "{table_name}" LIMIT 5').fetchdf()
             output_parts.append(sample.to_string(index=False))
@@ -465,7 +465,7 @@ def action_summary(
                     LIMIT 5
                 """).fetchall()
                 if top_vals:
-                    output_parts.append(f"  top values:")
+                    output_parts.append("  top values:")
                     for val, freq in top_vals:
                         pct = (freq / row_count * 100) if row_count > 0 else 0
                         output_parts.append(f"    {val}: {freq} ({pct:.1f}%)")