refactor: apply React best practices and migrate to ESLint CLI

- Dynamic import for WordCloud component (code splitting)
- Fix waterfall in handleRefresh with Promise.all
- Memoize data prep functions in overview page (7 useMemo hooks)
- Replace useState+useEffect with useMemo in CountryDisplay/LanguageDisplay
- Memoize navigationCards and class getters in dashboard page
- Extract inline handlers with useCallback
- Fix missing index parameter in TopQuestionsChart map
- Migrate from next lint to ESLint CLI (Next.js 16 deprecation)

components/CountryDisplay.tsx

@@ -1,6 +1,6 @@
 "use client";
 
-import { useEffect, useState } from "react";
+import { useMemo } from "react";
 import { getLocalizedCountryName } from "../lib/localization";
 
 interface CountryDisplayProps {
@@ -16,16 +16,11 @@ export default function CountryDisplay({
   countryCode,
   className,
 }: CountryDisplayProps) {
-  const [countryName, setCountryName] = useState<string>(
-    countryCode || "Unknown"
+  // Compute directly - Intl.DisplayNames is synchronous
+  const countryName = useMemo(
+    () => (countryCode ? getLocalizedCountryName(countryCode) : "Unknown"),
+    [countryCode]
   );
 
-  useEffect(() => {
-    // Only run in the browser and if we have a valid code
-    if (typeof window !== "undefined" && countryCode) {
-      setCountryName(getLocalizedCountryName(countryCode));
-    }
-  }, [countryCode]);
-
   return <span className={className}>{countryName}</span>;
 }