fix(index): %d can't format the "(all)" label-count fallback (#7)

Co-authored-by: claude <[email protected]>

rag/index.py

@@ -160,7 +160,7 @@ def main() -> int:
                 label_count += 1
                 last_label_key = key
         records.append(rec)
-    log.info("loaded %d chunks from %d label(s) in %.1fs",
+    log.info("loaded %d chunks from %s label(s) in %.1fs",
              len(records), label_count or "(all)", time.time() - t0)
 
     if args.bm25_only: