sfu: fix JanusClient info() endpoint URL (/info not /)

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

src/JanusClient.php

@@ -20,7 +20,7 @@ final class JanusClient
     /** GET /janus/info — returns server info or null. */
     public function info(): ?array
     {
-        return $this->get('');
+        return $this->get('/info');
     }
 
     /** Create a new Janus session. Returns session_id or null. */