feat: add Teams admin settings and group-based creation limits

[lennart441]

• Resolves: Allow restricting team-creation to certain groups #2717

Summary

Adds a Teams admin settings section where admins can restrict which Nextcloud groups may create teams. The restriction is enforced in the API and UI: create actions stay hidden without permission, and the empty-state copy no longer prompts users to create a team.

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
  no
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)

AI (if applicable)

• The content of this PR was partly or fully generated using AI
  Assisted by: Cursor:Grok-4.5

Screenshot of the teams app without permission to create a team

Admin settings of teams after

]

[jospoortvliet]

I would suggest we stick with the quota mgmt features rather than blocking creation of teams for some users:
nextcloud/groupfolders#4975

IF we want this feature, let's only allow configuring it in config.php, so that it's not the first thing admins might do when setting up Nextcloud, treating Nextcloud Teams like Microsoft Teams.

[mejo-]

I would suggest we stick with the quota mgmt features rather than blocking creation of teams for some users.

I agree. I think we do many Nextcloud users a favour if we take a bold stance here and don't allow to disable creation of teams.

[lennart441]

Closing in favor of #2743, which follows the config.php-based direction from the discussion here (no admin-UI kill-switch for team creation / team spaces).

Superseded by: #2743

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