Enable Circle/Team Admins to Create New User Accounts

Is your feature request related to a problem? Please describe.
Currently, only Nextcloud administrators can create user accounts. If a Team admin wants to invite someone not already in the system, they have to request that an administrator set up the new account first. This creates an extra step, slows down onboarding, and can result in duplicate accounts if the process isn’t carefully followed.

Describe the solution you’d like
Enable Circle/Team admins to register new user accounts directly. For example, in the Teams/Circles management UI, admins would see an option to “Add New User.” Once created, that user automatically belongs to the Circle/Team. An optional email invitation or verification process could be part of this workflow to ensure security.

This feature would make it significantly easier for communities or project teams using Nextcloud to self-manage membership.
A clear audit log or notification to global admins could maintain oversight, ensuring that new accounts are legitimate.
Ideally, Team admins should also be able to check if a user already exists in the system before creating a new one, helping avoid accidental duplicates.

Thank you for considering this feature! We appreciate all the hard work on Nextcloud Teams.

The issue names the Teams/Circles management UI as the entry point, but no files or tests. First map how Circle/Team admin permissions and existing account creation are represented, then agree on a bounded workflow and tests covering authorization, membership, duplicate checks, and any invitation or audit requirements.