Skip non-directory entries in cleanUp results folder

[SeaCelo]

Fixes #7

• Skip non-directory entries when iterating over the results folder during cleanUp(). Not an issue on Windows but a good patch to prevent errors on any future platforms.

Why

• On macOS, Finder creates .DS_Store files in folders.
• cleanUp() assumes every entry in res/ is a directory and crashes with NotADirectoryError when it hits .DS_Store.
• This guard avoids the error without changing any behavior on other platforms.

Testing

• Clicked CLEAN UP on macOS; no 500 error.