Upgrade Script to Latest PHP

I have a small, well-loved PHP 7.4 script that now needs to run flawlessly on the most recent stable PHP release. The code lives here for your review: https://gitlab.com/tfl-php-scripts/enthusiast.

The remit is straightforward: refactor or replace any deprecated language constructs, libraries, and extensions so the application installs and executes without warnings or errors on PHP 8.x (or whatever version is current at project start). All existing functionality must remain identical, and the original header comment that credits the first author must stay untouched.

Once the conversion is complete, I want the whole thing run through thorough manual testing—page by page, feature by feature—to confirm parity with the 7.4 build. Automated tests are welcome if they help you, but I will be signing off based on a manual walk-through.

Deliverables
• Updated codebase committed back to the repository (or delivered as a ZIP)
• Brief manual-testing checklist showing what you verified and the outcome
• A short change log summarising key incompatibilities you addressed

No new features or UI tweaks are needed; this is purely a version uplift.