fix: add missing _recentFilesCache and _recentRefreshTimer in config.js

frontend/js/config.js

@@ -1,6 +1,10 @@
 // config.js — extracted from app.js (3872-4865)
 import { selectedContextVault, allVaults, activeSidebarTab, sidebarFilterCaseSensitive } from './state.js';
 
+let _recentTimestampTimer = null;
+let _recentFilesCache = [];
+let _recentRefreshTimer = null;
+
 async function loadRecentFiles(vaultFilter) {
   const listEl = document.getElementById("recent-list");
   const emptyEl = document.getElementById("recent-empty");