fix: map chinese language requests to zh-CN

src/pages/admin/AdminResourceForm.tsx

@@ -54,7 +54,7 @@ export function AdminResourceForm() {
   const [err, setErr] = useState<string | null>(null);
 
   useEffect(() => {
-    getJSON<Category[]>("/api/categories?lang=zh")
+    getJSON<Category[]>("/api/categories?lang=zh-CN")
       .then(setCats)
       .catch(() => setCats([]));
   }, []);

src/pages/admin/AdminResources.tsx

@@ -32,7 +32,7 @@ export function AdminResources() {
   const [total, setTotal] = useState(0);
 
   useEffect(() => {
-    getJSON<Category[]>("/api/categories?lang=zh")
+    getJSON<Category[]>("/api/categories?lang=zh-CN")
       .then((cats) => {
         const m: Record<number, string> = {};
         for (const c of cats) m[c.id] = c.name;