fix(map): S57 ENC 오버레이 스타일 로드 완료 대기 후 레이어 추가

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

frontend/src/common/components/map/S57EncOverlay.tsx

@@ -137,14 +137,21 @@ export function S57EncOverlay({ visible }: S57EncOverlayProps) {
     if (!map) return;
 
     if (visible) {
-      addEncLayers(map);
+      const doAdd = () => addEncLayers(map);
+
+      if (map.isStyleLoaded()) {
+        doAdd();
+      } else {
+        map.once('style.load', doAdd);
+      }
+
+      return () => {
+        map.off('style.load', doAdd);
+        removeEncLayers(map);
+      };
     } else {
       removeEncLayers(map);
     }
-
-    return () => {
-      if (map) removeEncLayers(map);
-    };
   // eslint-disable-next-line react-hooks/exhaustive-deps
   }, [visible, mapRef]);