fix filename sanitization for directory names

[ShivamSingh47007]

issue (#113)
I created a pull request that replaces : with - in the generated directory name.
This should prevent filename issues when exporting files to Nextcloud.

the directory name was created using DateTime.now() which includes : characters

this change replaces : with - when creating the directory name

this helps avoid filename issues when exporting files to Nextcloud and other file systems

[veejayts]

Hi Shivam, thanks for volunteering to fix this issue.

I think the file name would be better if it the output was in the following format OpenScan-2026-08-23-1787479053634 since it is cleaner and avoid any other characters like period that the current file name generates.

OpenScan-yyyy-mm-dd-millisecondsSinceEpoch

If it is changed to that, I can sanity test it once and merge it.