create custom redirection for expired URL

[UnelDev]

Summary

feature that allows custom redirection specifically for expired short URLs.
This could be done either through an environment variable (e.g. EXPIRED_SHORT_URL) or via redirect rules that are triggered only when a short URL has expired.

Use case

When I share short links with an expiration date, users often contact me saying the link "doesn't work" — while in reality, the link is just expired.
Currently, expired URLs return a generic 404 error, which is indistinguishable from invalid or non-existent short codes.

Having a way to handle expired links separately would:

• Improve user experience with a clear message (e.g. "This link has expired")
• Reduce confusion between invalid and expired URLs

Thank you for considering this feature!