SpEc012/VenChecker ? reverse-engineered prompt

I found this old Python project and I want you to turn it into something safe and actually usable. Please rebuild it as a simple local tool that works with a sample list of usernames or account names from a text file and labels them as valid format, invalid format, duplicate, or missing based on clear rules we define in the app.

Clean up the old code, remove anything that tries to hit real Venmo accounts or do any kind of login checking, and fix the broken parts so it runs reliably. I want clear output, basic logging, friendly error messages, and a simple way to load a file and save results. If it makes sense, add a small demo interface or keep it as a clean command line app, whichever is easier and more polished.

Please include a sample input file, a short readme with setup steps, and a note that this is only for local validation and testing. You can look up current docs online if you need to.