Fix Codex Responses API base URL

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

internal/gateway/handlers.go

@@ -235,7 +235,7 @@ func (s *Server) applyCodex(w http.ResponseWriter, id string) {
 		return
 	}
 	injection, err := mgr.Apply(codexcfg.ApplyOptions{
-		BaseURL: fmt.Sprintf("http://127.0.0.1:%d", s.port),
+		BaseURL: fmt.Sprintf("http://127.0.0.1:%d/v1", s.port),
 		Token:   s.store.Config().RelayToken,
 	})
 	if err != nil {