Preserve the last good shared snapshot until a replacement is fully staged, and proactively remove stale snapshot_temp_* directories left behind by interrupted snapshot attempts. This prevents orphaned temp snapshots from accumulating while avoiding false cleanup errors after successful promotion.
Changelog-Fixed: Fixed issue where temporary files would not get cleaned up
Closes: https://github.com/damus-io/damus/issues/3684
Signed-off-by: Daniel D’Aquino <daniel@daquino.me>