fix(script): enforce script body limits without streaming

Streaming accepted a chunked body cut at a chunk boundary as complete,
so the limit now comes from the client that reads the body, picked per
requested size. Script requests keep their own default, maxBodySize
accepts sizes like 10MiB, and files sarin downloads for itself are
capped at 64MiB.

internal/script/script.go

@@ -171,10 +171,13 @@ func fetchURL(ctx context.Context, url string) (string, error) {
 		return "", types.NewHTTPStatusError(url, resp.StatusCode, resp.Status)
 	}
 
-	data, err := io.ReadAll(resp.Body)
+	data, err := io.ReadAll(io.LimitReader(resp.Body, types.RemoteFetchLimit+1))
 	if err != nil {
 		return "", types.NewHTTPFetchError(url, err)
 	}
+	if len(data) > types.RemoteFetchLimit {
+		return "", types.NewHTTPFetchError(url, types.ErrRemoteFileTooLarge)
+	}
 
 	return string(data), nil
 }