Feat: Support for Time-Limited (Expiring) Links

**Is your feature request related to a problem? Please describe.**
At the moment, all created links in SmartyURL are permanent. There is no option to set an expiry period or an expiry date. This can be an issue when we want to create time-limited links without manually removing them later. It also means expired links continue to redirect normally even when they should no longer be valid.

**Describe the solution you'd like**
I would like to have an option, when creating or editing a link, to choose whether the link is:
- Permanent, or
- Time-limited

If the link is time-limited, the user should be able to:
- Set the number of days before the link expires, or
- Select a specific expiry date from a date picker

Once a link reaches its expiry date, it should stop redirecting and instead show an "Expired link" message. The link should remain stored in the database and not be deleted automatically unless the admin specifically enables automatic deletion.

**Describe alternatives you've considered**
The only current workaround is manually checking and deleting old links, which is not practical. Another option is building a custom script to disable expired links, but this would be outside SmartyURL and harder to maintain.

**Additional context**
It would be useful to have a system setting that controls what happens to expired links:
- If the setting is enabled: a scheduled cron job will automatically delete expired links.
- If the setting is disabled: the cron job will keep expired links without deleting them.

This provides flexibility for different use cases and keeps the database clean when needed.