Add “Last checked” information

[PaulKappmeyer]

Is your feature request related to a problem? Please describe.
No related problem.

Describe the solution you'd like
It would be great to have a small text or label in the Update Manager that shows the date and time of the last update check or the last performed update. For example:

• “Last checked: 2025-10-06 14:32”
• “Last update: 2 days ago”
  This would make it easier for users to see at a glance when their system was last refreshed.

Describe alternatives you've considered
I’ve considered checking the logs or using command-line tools to see when updates were last checked, but that’s less convenient and not very user-friendly for beginners.

Additional context
I think this feature would be really easy to implement, while still adding to the usability, especially for beginners.

[PaulKappmeyer]

If this feature would be considered useful, i could also think of trying to implement this feature on my own since i would like to get into open source, but it would take some time to look into the code.