`fileblob` creates temp files in `os.TempDir()` (`/tmp`) by default,
then uses `os.Rename` to move them to the final path. When the storage
directory is on a different filesystem (e.g. a Docker volume mount at
`/data`), the rename fails with "invalid cross-device link".
Set `no_tmp_dir=true` on file:// bucket URLs so fileblob creates temp
files next to the final destination instead.
Fixes#65