Visually distinguish users from contacts (e.g. with an icon)

Is your feature request related to a problem? Please describe.

Although I'm a (very) regular user of Nextcloud, it took me a while to figure out why I sometimes had duplicate contacts; I finally realized that some of the contacts in my contact list are actually the platform users I'm allowed to interact with via the platform. I think this lacks clarity and that these "users" (who are read-only) should carry a visual distinction sign. See attached screenshot (test made with my browser's development tools), with user icon displayed in front of the users ("fake" contacts).

I would have tried to do a Pull Request myself, but getting my hands into Nextcloud Vue with all these generic elements centralized, I always feel that if I touch something, it's going to have plenty of side effects in other places of the user interface (collateral damage).

Describe the solution you'd like

See first paragraph.

Describe alternatives you've considered

None.

Additional context

No response

Start by locating the contact-list UI and the Nextcloud Vue generic elements that render platform users as read-only contacts. Add a visual distinction such as the user icon shown in the issue, then verify that users are clearly separated from regular contacts without changing unrelated shared components.