Fix join page media upload TypeScript build error.

Co-authored-by: Cursor <cursoragent@cursor.com>

app/[locale]/join/page.tsx

@@ -456,10 +456,11 @@ export default function JoinPage() {
                     "/api/upload-media",
                     { method: "POST", body: fd }
                   );
-                  if (!data?.ok) {
+                  if (!data?.ok || !data.url) {
                     throw new Error(data?.error || "上传失败");
                   }
-                  setMedia((m) => (m ? { ...m, url: data.url } : null));
+                  const uploadedUrl = data.url;
+                  setMedia((m) => (m ? { ...m, url: uploadedUrl } : null));
                 } catch (err) {
                   alert(err instanceof Error ? err.message : "上传失败");
                   URL.revokeObjectURL(preview);